                       Kea Administrator Reference Manual

   This is the reference guide for Kea version 0.9.1.

   Copyright (c) 2010-2015 Internet Systems Consortium, Inc.

   Abstract

   Kea is an open source implementation of the Dynamic Host Configuration
   Protocol (DHCP) servers, developed and maintained by Internet Systems
   Consortium (ISC).

   This is the reference guide for Kea version 0.9.1. The most up-to-date
   version of this document (in PDF, HTML, and plain text formats), along
   with other documents for Kea, can be found at http://kea.isc.org/docs.

   --------------------------------------------------------------------------

   Table of Contents

   1. Introduction

                1.1. Supported Platforms

                1.2. Required Software at Run-time

                1.3. Kea Software

   2. Quick start

                2.1. Quick start guide for DHCPv4 and DHCPv6 services

                2.2. Running Kea servers directly

   3. Installation

                3.1. Packages

                3.2. Install Hierarchy

                3.3. Building Requirements

                3.4. Installation from Source

                             3.4.1. Download Tar File

                             3.4.2. Retrieve from Git

                             3.4.3. Configure before the build

                             3.4.4. Build

                             3.4.5. Install

                3.5. Selecting the Configuration Backend

                3.6. DHCP Database Installation and Configuration

                             3.6.1. Building with MySQL Support

                             3.6.2. Building with PostgreSQL support

   4. Kea Database Administration

                4.1. Databases and Database Version Numbers

                4.2. The kea-admin Tool

                4.3. Supported Databases

                             4.3.1. memfile

                             4.3.2. MySQL

                             4.3.3. PostgreSQL

                             4.3.4. Limitations related to the use of the SQL
                             databases

   5. Kea configuration

                5.1. BUNDY configuration backend

                5.2. JSON configuration backend

                             5.2.1. JSON syntax

                             5.2.2. Simplified Notation

   6. Managing Kea with keactrl

                6.1. Overview

                6.2. Command Line Options

                6.3. The keactrl Configuration File

                6.4. Commands

                6.5. Overriding the Server Selection

   7. The DHCPv4 Server

                7.1. Starting and Stopping the DHCPv4 Server

                7.2. DHCPv4 Server Configuration

                             7.2.1. Introduction

                             7.2.2. Lease Storage

                             7.2.3. Interface configuration

                             7.2.4. IPv4 Subnet Identifier

                             7.2.5. Configuration of IPv4 Address Pools

                             7.2.6. Standard DHCPv4 options

                             7.2.7. Custom DHCPv4 options

                             7.2.8. DHCPv4 Vendor Specific Options

                             7.2.9. Nested DHCPv4 Options (Custom Option
                             Spaces)

                             7.2.10. Unspecified parameters for DHCPv4 option
                             configuration

                             7.2.11. Stateless Configuration of DHCPv4
                             clients

                             7.2.12. Client Classification in DHCPv4

                             7.2.13. Configuring DHCPv4 for DDNS

                             7.2.14. Next Server (siaddr)

                             7.2.15. Echoing Client-ID (RFC 6842)

                7.3. Host reservation in DHCPv4

                             7.3.1. Address reservation types

                             7.3.2. Conflicts in DHCPv4 reservations

                             7.3.3. Reserving a hostname

                             7.3.4. Reserving specific options

                             7.3.5. Fine Tuning IPv4 Host Reservation

                7.4. Server Identifier in DHCPv4

                7.5. How the DHCPv4 Server Selects a Subnet for the Client

                             7.5.1. Using a Specific Relay Agent for a Subnet

                             7.5.2. Segregating IPv4 Clients in a Cable
                             Network

                7.6. Supported DHCP Standards

                7.7. DHCPv4 Server Limitations

   8. The DHCPv6 Server

                8.1. Starting and Stopping the DHCPv6 Server

                8.2. DHCPv6 Server Configuration

                             8.2.1. Introduction

                             8.2.2. Lease Storage

                             8.2.3. Interface selection

                             8.2.4. IPv6 Subnet Identifier

                             8.2.5. Unicast traffic support

                             8.2.6. Subnet and Address Pool

                             8.2.7. Subnet and Prefix Delegation Pools

                             8.2.8. Standard DHCPv6 options

                             8.2.9. Custom DHCPv6 options

                             8.2.10. DHCPv6 vendor specific options

                             8.2.11. Nested DHCPv6 options (custom option
                             spaces)

                             8.2.12. Unspecified parameters for DHCPv6 option
                             configuration

                             8.2.13. IPv6 Subnet Selection

                             8.2.14. DHCPv6 Relays

                             8.2.15. Relay-Supplied Options

                             8.2.16. Client Classification in DHCPv6

                             8.2.17. Limiting access to IPv6 subnet to
                             certain classes

                             8.2.18. Configuring DHCPv6 for DDNS

                8.3. Host reservation in DHCPv6

                             8.3.1. Address/prefix reservation types

                             8.3.2. Conflicts in DHCPv6 reservations

                             8.3.3. Reserving a hostname

                             8.3.4. Reserving specific options

                             8.3.5. Fine Tuning IPv6 Host Reservation

                8.4. Server Identifier in DHCPv6

                8.5. Stateless DHCPv6 (Information-Request Message)

                8.6. Using specific relay agent for a subnet

                8.7. Segregating IPv6 clients in a cable network

                8.8. MAC/Hardware addresses in DHCPv6

                8.9. Supported DHCPv6 Standards

                8.10. DHCPv6 Server Limitations

   9. The DHCP-DDNS Server

                9.1. Starting and Stopping the DHCP-DDNS Server

                9.2. Configuring the DHCP-DDNS Server

                             9.2.1. Global Server Parameters

                             9.2.2. TSIG Key List

                             9.2.3. Forward DDNS

                             9.2.4. Reverse DDNS

                             9.2.5. Example DHCP-DDNS Server Configuration

                9.3. DHCP-DDNS Server Limitations

   10. The LFC process

                10.1. Overview

                10.2. Command Line Options

   11. Hooks Libraries

                11.1. Introduction

                11.2. Configuring Hooks Libraries

   12. libdhcp++ library

                12.1. Interface detection and Socket handling

   13. Logging

                13.1. Logging Configuration

                             13.1.1. Loggers

                             13.1.2. Output Options

                             13.1.3. Example Logger Configurations

                13.2. Logging Message Format

                13.3. Logging During Kea Startup

   14. Acknowledgements

   List of Tables

   7.1. List of standard DHCPv4 options

   7.2. List of standard DHCPv4 options (continued)

   7.3. List of standard DHCP option types

   7.4. Default FQDN Flag Behavior

   8.1. List of standard DHCPv6 options

   8.2. Default FQDN Flag Behavior

   9.1. Our example network

   9.2. Forward DDNS Domains Needed

   9.3. Reverse DDNS Domains Needed

Chapter 1. Introduction

   Table of Contents

   1.1. Supported Platforms

   1.2. Required Software at Run-time

   1.3. Kea Software

   Kea is the next generation of DHCP software developed by ISC. It supports
   both DHCPv4 and DHCPv6 protocols along with their extensions, e.g. prefix
   delegation and dynamic updates to DNS.

   Kea was initially developed as a part of the BIND 10 framework. In early
   2014, ISC made the decision to discontinue active development of BIND 10
   and continue development of Kea as standalone DHCP software.

   This guide covers Kea version 0.9.1.

1.1. Supported Platforms

   Kea is officially supported on RedHat Enterprise Linux, CentOS, Fedora and
   FreeBSD systems. It is also likely to work on many other platforms: builds
   have been tested on (in no particular order) Debian GNU/Linux 6 and
   unstable, Ubuntu 9.10, NetBSD 5, Solaris 10 and 11, FreeBSD 7 and 8,
   CentOS Linux 5.3, MacOS 10.6 and 10.7, and OpenBSD 5.1. Non supported
   systems (especially non-Linux) are likely to have issues with directly
   connected DHCPv4 clients.

   There are currently no plans to port Kea to Windows platforms.

1.2. Required Software at Run-time

   Running Kea uses various extra software which may not be provided in the
   default installation of some operating systems, nor in the standard
   package collections. You may need to install this required software
   separately. (For the build requirements, also see Section 3.3, "Building
   Requirements".)

     o Kea supports two crypto libraries: Botan and OpenSSL. Only one of them
       is required to be installed during compilation. Kea uses the Botan
       crypto library for C++ (http://botan.randombit.net/), version 1.8 or
       later. As an alternative to Botan, Kea can use the OpenSSL crypto
       library (http://www.openssl.org/). It requires a version with SHA-2
       support.
     o Kea uses the log4cplus C++ logging library
       (http://log4cplus.sourceforge.net/). It requires at least log4cplus
       version 1.0.3.
     o In order to store lease information in a MySQL database, Kea requires
       MySQL headers and libraries. This is an optional dependency in that
       Kea can be built without MySQL support.
     o In order to store lease information in a PostgreSQL database, Kea
       requires PostgreSQL headers and libraries. This is an optional
       dependency in that Kea can be built without PostgreSQL support.

1.3. Kea Software

   Kea is modular. Part of this modularity is accomplished using multiple
   cooperating processes which, together, provide the server functionality.
   The following software is included with Kea:

     o keactrl -- Tool to start, stop, reconfigure, and report status for the
       Kea servers.
     o kea-dhcp4 -- DHCPv4 server process. This process responds to DHCPv4
       queries from clients.
     o kea-dhcp6 -- DHCPv6 server process. This process responds to DHCPv6
       queries from clients.
     o kea-dhcp-ddns -- DHCP-DDNS process. This process acts as an
       intermediary between the DHCP servers and DNS server. It receives name
       update requests from the DHCP servers and sends DNS Update messages to
       the DNS servers.
     o kea-admin -- A tool useful for database backend maintenance (creating
       new database, checking versions, upgrading etc.)
     o kea-lfc -- This process removes redundant information from the files
       used to provide persistent storage for the memfile data base backend.
       The service is written to run as a stand alone process. While it can
       be started externally it should be started by the Kea DHCP servers.
     o perfdhcp -- DHCP benchmarking tool which simulates multiple clients to
       test both DHCPv4 and DHCPv6 servers performance.

   The tools and modules are covered in full detail in this guide. In
   addition, manual pages are also provided in the default installation.

   Kea also provides C++ libraries and programmer interfaces for DHCP. These
   include detailed developer documentation and code examples.

Chapter 2. Quick start

   Table of Contents

   2.1. Quick start guide for DHCPv4 and DHCPv6 services

   2.2. Running Kea servers directly

   This quickly covers the standard steps for installing and deploying Kea.
   For further details, full customizations, and troubleshooting, see the
   respective chapters in the Kea guide.

2.1. Quick start guide for DHCPv4 and DHCPv6 services

    1. Install required run-time and build dependencies. See Section 3.3,
       "Building Requirements" for details.
    2. Download Kea source tarball from ISC.org downloads page or ISC ftp
       server.

    3. Extract the tarball. For example:

 $ tar xvzf kea-0.9.1.tar.gz

    4. Go into the source directory and run the configure script:

 $ cd kea-0.9.1
 $ ./configure [your extra parameters]

    5. Build it:

 $ make

    6. Install it (by default the installation prefix is /usr/local/, so you
       likely need root privileges for that step):

 # make install

    7. Edit the configuration file which by default is installed in
       [kea-install-dir]/etc/kea/kea.conf and contains configuration for all
       Kea services. Configuration choices for DHCPv4 and DHCPv6 services are
       described in Section 7.2, "DHCPv4 Server Configuration" and
       Section 8.2, "DHCPv6 Server Configuration", respectively.

    8. In order to start the DHCPv4 server in background, run the following
       command (as root):

 # keactrl start -s dhcp4

       Or run the following command to start DHCPv6 server instead:

 # keactrl start -s dhcp6

       Note that it is also possible to start both servers simultaneously:

 $ keactrl start

    9. Verify that Kea server(s) are running:

 # keactrl status

       If the server status is "inactive" may indicate a configuration error.
       Please check a log file (by default located in
       [kea-install-dir]/var/kea/kea.log) for the details of the error.

   10. If the server has been started sucessfully, test that it is responding
       to DHCP queries and that the client receives a configuration from the
       server; for example, use the ISC DHCP client.

   11. Stop running server(s):

 # keactrl stop

   For more system specific installation procedures, you may want to visit
   System specific notes, available on Kea homepage.

   The details of keactrl script usage can be found in Chapter 6, Managing
   Kea with keactrl.

2.2. Running Kea servers directly

   Kea servers can be started directly (without a need to use keactrl). To
   start DHCPv4 server run the following commmand:

 # kea-dhcp4 -c /path/to/your/kea4/config/file.json

   And, to start the DHCPv6 server run the following command:

 # kea-dhcp6 -c /path/to/your/kea6/config/file.json

Chapter 3. Installation

   Table of Contents

   3.1. Packages

   3.2. Install Hierarchy

   3.3. Building Requirements

   3.4. Installation from Source

                3.4.1. Download Tar File

                3.4.2. Retrieve from Git

                3.4.3. Configure before the build

                3.4.4. Build

                3.4.5. Install

   3.5. Selecting the Configuration Backend

   3.6. DHCP Database Installation and Configuration

                3.6.1. Building with MySQL Support

                3.6.2. Building with PostgreSQL support

3.1. Packages

   Some operating systems or software package vendors may provide
   ready-to-use, pre-built software packages for Kea. Installing a pre-built
   package means you do not need to install build-only prerequisites and do
   not need to make the software.

   FreeBSD ports, NetBSD pkgsrc, and Debian testing package collections
   provide all the prerequisite packages.

3.2. Install Hierarchy

   The following is the directory layout of the complete Kea installation
   (all directories paths are relative to the installation directory):

     o etc/kea/ -- configuration files.
     o include/ -- C++ development header files.
     o lib/ -- libraries.
     o sbin/ -- server software and commands used by the system
       administrator.
     o share/kea/ -- configuration specifications and examples.
     o share/doc/kea/ -- this guide, other supplementary documentation, and
       examples.
     o share/man/ -- manual pages (online documentation).
     o var/kea/ -- server identification, lease databases, and log files.

3.3. Building Requirements

   In addition to the run-time requirements (listed in Section 1.2, "Required
   Software at Run-time"), building Kea from source code requires various
   development include headers and program development tools.

  Note

   Some operating systems have split their distribution packages into a
   run-time and a development package. You will need to install the
   development package versions, which include header files and libraries, to
   build Kea from the source code.

   Building from source code requires the following software installed on the
   system:

     o Boost build-time headers (http://www.boost.org/). At least Boost
       version 1.35 is required.

     o Botan (at least version 1.8) or OpenSSL.

     o log4cplus (at least version 1.0.3) development include headers.

     o A C++ compiler and standard development headers. Kea builds have been
       tested with GCC g++ 3.4.3, 4.1.2, 4.1.3, 4.2.1, 4.3.2, and 4.4.1;
       Clang++ 2.8; and Sun C++ 5.10.

     o The development tools "make".

   Visit the user-contributed wiki at
   http://kea.isc.org/wiki/SystemSpecificNotes for system-specific
   installation tips.

3.4. Installation from Source

   Kea is open source software written in C++. It is freely available in
   source code form from ISC as a downloadable tar file or via Kea Git code
   revision control service. (It may also be available in pre-compiled
   ready-to-use packages from operating system vendors.)

  3.4.1. Download Tar File

   The Kea release tarballs may be downloaded from:
   http://ftp.isc.org/isc/kea/ (using FTP or HTTP).

  3.4.2. Retrieve from Git

   Downloading this "bleeding edge" code is recommended only for developers
   or advanced users. Using development code in a production environment is
   not recommended.

  Note

   When building from source code retrieved via Git, additional software will
   be required: automake (v1.11 or later), libtoolize, and autoconf (2.59 or
   later). These may need to be installed.

   The latest development code (together with temporary experiments and
   un-reviewed code) is available via the Kea code revision control system.
   This is powered by Git and all the Kea development is public. The leading
   development is done in the "master" branch.

   The code can be checked out from git://git.kea.isc.org/kea:

 $ git clone git://git.kea.isc.org/kea

   The code checked out from the git repository doesn't include the generated
   configure script, Makefile.in files, nor their related build files. They
   can be created by running autoreconf with the --install switch. This will
   run autoconf, aclocal, libtoolize, autoheader, automake, and related
   commands.

  3.4.3. Configure before the build

   Kea uses the GNU Build System to discover build environment details. To
   generate the makefiles using the defaults, simply run:

 $ ./configure

   Run ./configure with the --help switch to view the different options. Some
   commonly-used options are:

   --prefix
           Define the installation location (the default is /usr/local).

   --with-boost-include
           Define the path to find the Boost headers.

   --with-botan-config
           To specific the path to the botan-config script to build with
           Botan for the crypto code.

   --with-gtest
           Enable the building of the C++ Unit Tests using the Google Test
           framework. Optionally this can define the path to the gtest header
           files and library. (If the framework is not already installed on
           your system, it can be downloaded from
           https://code.google.com/p/googletest.)

   --with-log4cplus
           Define the path to find the Log4cplus headers and libraries.

   --with-openssl
           Replace Botan by OpenSSL for the crypto library. The default is to
           try to find a working Botan then OpenSSL only if Botan is not
           found.

   --without-werror
           Disable the default use of the -Werror compiler flag so that
           compiler warnings do not result in build failures.

  Note

   For additional instructions concerning the building and installation of
   Kea for various databases, see Section 3.6, "DHCP Database Installation
   and Configuration". For additional instructions concerning the
   configuration backends, see Section 3.5, "Selecting the Configuration
   Backend".

   For example, the following command configures Kea to find the Boost
   headers in /usr/pkg/include, specifies that PostgreSQL support should be
   enabled, and sets the installation location to /opt/kea:

 $ ./configure \
       --with-boost-include=/usr/pkg/include \
       --with-dhcp-pgsql=/usr/local/bin/pg_config \
       --prefix=/opt/kea

   If the configure fails, it may be due to missing or old dependencies.

  3.4.4. Build

   After the configure step is complete, build the executables from the C++
   code and prepare the Python scripts by running the command:

 $ make

  3.4.5. Install

   To install the Kea executables, support files, and documentation, issue
   the command:

 $ make install

   Do not use any form of parallel or job server options (such as GNU make's
   -j option) when performing this step: doing so may cause errors.

  Note

   The install step may require superuser privileges.

   If required, run ldconfig as root with /usr/local/lib (or with
   ${prefix}/lib if configured with --prefix) in /etc/ld.so.conf (or the
   relevant linker cache configuration file for your OS):

 $ ldconfig

  Note

   If you do not run ldconfig where it is required, you may see errors like
   the following:

               program: error while loading shared libraries: libkea-something.so.1:
               cannot open shared object file: No such file or directory


3.5. Selecting the Configuration Backend

   Kea 0.9 has introduced configuration backends that are switchable during
   the compilation phase. The backend is chosen using the --with-kea-config
   switch when running the configure script. It currently supports two
   values: BUNDY and JSON. JSON is the default.

   BUNDY
           BUNDY means that Kea is linked with the Bundy configuration
           backend that connects to the Bundy framework and in general works
           exactly the same as Kea 0.8 and earlier BIND10 versions. The
           benefits of that backend are uniform integration with the Bundy
           framework, easy on-line reconfiguration using bindctl, available
           RESTful API. On the other hand, it requires the whole heavy Bundy
           framework that requires Python3 to be present. That backend is
           likely to go away with the release of Kea 1.0.

   JSON
           JSON is the new default configuration backend that causes Kea to
           read JSON configuration files from disk. It does not require any
           framework and thus is considered more lightweight. It will allow
           dynamic on-line reconfiguration, but will lack remote capabilities
           (i.e. no RESTful API).

3.6. DHCP Database Installation and Configuration

   Kea stores its leases in a lease database. The software has been written
   in a way that makes it possible to choose which database product should be
   used to store the lease information. At present, Kea supports three
   database backends: MySQL, PostgreSQL and Memfile. To limit external
   dependencies, both MySQL and PostgreSQL support are disabled by default
   and only Memfile is available. Support for the optional external database
   backend must be explicitly included when Kea is built. This section covers
   the building of Kea with MySQL and/or PostgreSQL and the creation of the
   lease database.

  3.6.1. Building with MySQL Support

   Install MySQL according to the instructions for your system. The client
   development libraries must be installed.

   Build and install Kea as described in Chapter 3, Installation, with the
   following modification. To enable the MySQL database code, at the
   "configure" step (see Section 3.4.3, "Configure before the build"), do:

 ./configure [other-options] --with-dhcp-mysql

   Or specify the location of the MySQL configuration program "mysql_config"
   if MySQL was not installed in the default location:

 ./configure [other-options] --with-dhcp-mysql=path-to-mysql_config

   See Section 4.3.2.1, "First Time Creation of Kea Database" for details
   regarding MySQL database configuration.

  3.6.2. Building with PostgreSQL support

   Install PostgreSQL according to the instructions for your system. The
   client development libraries must be installed. Client development
   libraries are often packaged as "libpq".

   Build and install Kea as described in Chapter 3, Installation, with the
   following modification. To enable the PostgreSQL database code, at the
   "configure" step (see Section 3.4.3, "Configure before the build"), do:

 ./configure [other-options] --with-dhcp-pgsql

   Or specify the location of the PostgreSQL configuration program
   "pg_config" if PostgreSQL was not installed in the default location:

 ./configure [other-options] --with-dhcp-pgsql=path-to-pg_config

   See Section 4.3.3.1, "Manually Create the PostgreSQL Database and the Kea
   User" for details regarding PostgreSQL database configuration.

Chapter 4. Kea Database Administration

   Table of Contents

   4.1. Databases and Database Version Numbers

   4.2. The kea-admin Tool

   4.3. Supported Databases

                4.3.1. memfile

                4.3.2. MySQL

                4.3.3. PostgreSQL

                4.3.4. Limitations related to the use of the SQL databases

4.1. Databases and Database Version Numbers

   Kea stores leases in one of several supported databases. As future
   versions of Kea are released, the structure of those databases will
   change. For example, Kea currently only stores lease information: in the
   future, additional data - such as host reservation details - will also be
   stored.

   A given version of Kea expects a particular structure in the database. It
   ensures this by checking the version of the database it is using. Separate
   version numbers are maintained for backend databases, independent of the
   version of Kea itself. It is possible that the backend database version
   will stay the same through several Kea revisions. Likewise, it is possible
   that the version of backend database may go up several revisions during a
   Kea upgrade. Versions for each database are independent, so an increment
   in the MySQL database version does not imply an increment in that of
   PostgreSQL.

   Backend versions are specified in a major.minor format. The minor number
   is increased when there are backward compatibile changes introduced. For
   example, the addition of a new index. It is desirable, but not mandatory
   to to apply such a change; you can run on older database version if you
   want to. (Although, in the example given, running without the new index
   may be at the expense of a performance penalty.) On the other hand, the
   major number is increased when an incompatible change is introduced, for
   example an extra column is added to a table. If you try to run Kea
   software on a database that is too old (as signified by mismatched backend
   major version number), Kea will refuse to run: administrative action will
   be required to upgrade the database.

4.2. The kea-admin Tool

   To manage the databases, Kea provides the kea-admin tool. It is able to
   initialize a new database, check its version number, and perform a
   database upgrade.

   kea-admin takes two mandatory parameters: command and backend. Additional,
   non-mandatory options may be specified. Currently supported commands are:

     o lease-init -- Initializes a new lease database. Useful during first
       Kea installation. The database is initialized to the latest version
       supported by the version of the software.
     o lease-version -- Reports the lease database version number. This is
       not necessarily equal to the Kea version number as each backend has
       its own versioning scheme.
     o lease-upgrade -- Conducts a lease database upgrade. This is useful
       when upgrading Kea.

   backend specifies the backend type. Currently supported types are:

     o memfile -- Lease information is stored on disk in a text file.
     o mysql -- Lease information is stored in a MySQL relational database.
     o pgsql -- Lease information is stored in a PostgreSQL relational
       database.

   Additional parameters may be needed, depending on your setup and specific
   operation: username, password and database name or the directory where
   specific files are located. See appropriate manual page for details (man 8
   kea-admin).

4.3. Supported Databases

  4.3.1. memfile

   There are no special initialization steps necessary for the memfile
   backend. During the first run, both kea-dhcp4 and kea-dhcp6 will create an
   empty lease file if one is not present. Necessary disk write permission is
   required.

  4.3.2. MySQL

   The MySQL database must be properly set up if you want Kea to store
   information in MySQL. This section can be safely ignored if you chose to
   store the data in other backends.

    4.3.2.1. First Time Creation of Kea Database

   If you are setting the MySQL database for the first time, you need to
   create the database area within MySQL and set up the MySQL user ID under
   which Kea will access the database. This needs to be done manually:
   kea-admin is not able to do this for you.

   To create the database:

    1. Log into MySQL as "root":

 $ mysql -u root -p
 Enter password:
 mysql>

    2. Create the MySQL database:

 mysql> CREATE DATABASE database-name;

       (database-name is the name you have chosen for the database.)

    3. Create the user under which Kea will access the database (and give it
       a password), then grant it access to the database tables:

 mysql> CREATE USER 'user-name'@'localhost' IDENTIFIED BY 'password';
 mysql> GRANT ALL ON database-name.* TO 'user-name'@'localhost';

       (user-name and password are the user ID and password you are using to
       allow Keas access to the MySQL instance. All apostrophes in the
       command lines above are required.)

    4. At this point, you may elect to create the database tables.
       (Alternatively, you can exit MySQL and create the tables using the
       kea-admin tool, as explained below.) To do this:

 mysql> CONNECT database-name;
 mysql> SOURCE path-to-kea/share/kea/scripts/mysql/dhcpdb_create.mysql

       (path-to-kea is the location where you installed Kea.)

    5. Exit MySQL:

 mysql> quit
 Bye
 $

   If you elected not to create the tables in step 4, you can do so now by
   running the kea-admin tool:

 $ kea-admin lease-init mysql -u database-user -p database-password -n database-name

   (Do not do this if you did create the tables in step 4.) kea-admin
   implements rudimentary checks: it will refuse to initialize a database
   that contains any existing tables. If you want to start from scratch, you
   must remove all data manually. (This process is a manual operation on
   purpose to avoid possibly irretrievable mistakes by kea-admin.)

    4.3.2.2. Upgrading a MySQL Database from an Earlier Version of Kea

   Sometimes a new Kea version may use newer database schema, so there will
   be a need to upgrade the existing database. This can be done using the
   kea-admin lease-upgrade command.

   To check the current version of the database, use the following command:

 $ kea-admin lease-version mysql -u database-user -p database-password -n database-name

   (See Section 4.1, "Databases and Database Version Numbers" for a
   discussion about versioning.) If the version does not match the minimum
   required for the new version of Kea (as described in the release notes),
   the database needs to be upgraded.

   Before upgrading, please make sure that the database is backed up. The
   upgrade process does not discard any data but, depending on the nature of
   the changes, it may be impossible to subsequently downgrade to an earlier
   version. To perform an upgrade, issue the following command:

 $ kea-admin lease-upgrade mysql -u database-user -p database-password -n database-name

  4.3.3. PostgreSQL

   A PostgreSQL database must be set up if you want Kea to store lease and
   other information in PostgreSQL. This step can be safely ignored if you
   are using other database backends.

    4.3.3.1. Manually Create the PostgreSQL Database and the Kea User

   The first task is to create both the lease database and the user under
   which the servers will access it. A number of steps are required:

    1. Log into PostgreSQL as "root":

 $ sudo -u postgres psql postgres
 Enter password:
 postgres=#

    2. Create the database:

 postgres=# CREATE DATABASE database-name;
 CREATE DATABASE
 postgres=#

       (database-name is the name you have chosen for the database.)

    3. Create the user under which Kea will access the database (and give it
       a password), then grant it access to the database:

 postgres=# CREATE USER user-name WITH PASSWORD 'password';
 CREATE ROLE
 postgres=#
 postgres=# GRANT ALL PRIVILEGES ON DATABASE database-name TO user-name;
 GRANT
 postgres=#

    4. Exit PostgreSQL:

 postgres=# \q
 Bye
 $

    5. Create the database tables using the new user's credentials and the
       dhcpdb_create.pgsql script supplied with Kea. After entering the
       following command, you will be prompted for the new user's password.
       When the command completes you will be returned to the shell prompt.
       You should see output similar to following:

 $ psql -d database-name -U user-name -f path-to-kea/share/kea/scripts/pgsql/dhcpdb_create.pgsql
 Password for user user-name:
 CREATE TABLE
 CREATE INDEX
 CREATE INDEX
 CREATE TABLE
 CREATE INDEX
 CREATE TABLE
 START TRANSACTION
 INSERT 0 1
 INSERT 0 1
 INSERT 0 1
 COMMIT
 CREATE TABLE
 START TRANSACTION
 INSERT 0 1
 COMMIT
 $

       (path-to-kea is the location where you installed Kea.)

       If instead you encounter an error like:

 psql: FATAL:  no pg_hba.conf entry for host "[local]", user "user-name", database "database-name", SSL off

       ... you will need to alter the PostgreSQL configuration. Kea uses
       password authentication when connecting to the database and must have
       the appropriate entries added to PostgreSQL's pg_hba.conf file. This
       file is normally located in the primary data directory for your
       PostgreSQL server. The precise path may vary but the default location
       for PostgreSQL 9.3 on Centos 6.5 is:
       /var/lib/pgsql/9.3/data/pg_hba.conf.

       Assuming Kea is running on the same host as PostgreSQL, adding lines
       similar to following should be sufficient to provide
       password-authenticated access to Kea's database:

 local   database-name    user-name                                 password
 host    database-name    user-name          127.0.0.1/32           password
 host    database-name    user-name          ::1/128                password

       Please consult your PostgreSQL user manual before making these changes
       as they may expose your other databases that you run on the same
       system.

    4.3.3.2. Initialize the PostgreSQL Database Using kea-admin

   Support for PostgreSQL in kea-admin is currently not implemented.

  4.3.4. Limitations related to the use of the SQL databases

   The lease expiration time is stored in the SQL database for each lease as
   a timestamp value. Kea developers observed that MySQL database doesn't
   accept timestamps beyond 2147483647 seconds (maximum signed 32-bit number)
   from the beginning of the epoch. At the same time, some versions of
   PostgreSQL do accept greater values but the value is altered when it is
   read back. For this reason the lease database backends put the restriction
   for the maximum timestamp to be stored in the database, which is equal to
   the maximum signed 32-bit number. This effectively means that the current
   Kea version can't store the leases which expiration time is later than
   2147483647 seconds since the beginning of the epoch (around year 2038).

Chapter 5. Kea configuration

   Table of Contents

   5.1. BUNDY configuration backend

   5.2. JSON configuration backend

                5.2.1. JSON syntax

                5.2.2. Simplified Notation

   Depending on the configuration backend chosen (see Section 3.5, "Selecting
   the Configuration Backend"), the configuration mechanisms are different.
   The following sections describe details of the different configuration
   backends. Note that only one configuration backend can be used and its
   selection is made when the configure script is run.

5.1. BUNDY configuration backend

   This legacy configuration backend allows Kea to use the former BIND 10
   framework. That framework and this Kea configuration backend is no longer
   supported by ISC. It is currently developed as part of the Bundy project
   (see Bundy homepage). See the Bundy project documentation regarding
   configuration.

5.2. JSON configuration backend

   JSON is the default configuration backend. It assumes that the servers are
   started from the command line (either directly or using a script, e.g.
   keactrl). The JSON backend uses certain signals to influence Kea. The
   configuration file is specified upon startup using the -c parameter.

  5.2.1. JSON syntax

   Configuration files for DHCPv4, DHCPv6 and DDNS modules are defined in an
   extended JSON format. Basic JSON is defined in RFC 4627. Kea components
   use a slightly modified JSON, in that they allow shell-style comments in
   the file: lines with the hash (#) character in the first column are
   comment lines and are ignored.

   The configuration file consists of a single object (often colloquially
   called a map) started with a curly bracket. It comprises the "Dhcp4",
   "Dhcp6", "DhcpDdns" and/or "Logging" objects. It is possible to define
   additional elements, but they will be ignored. For example, it is possible
   to define Dhcp4, Dhcp6 and Logging elements in a single configuration file
   that can be used to start both the DHCPv4 and DHCPv6 components. When
   starting, the DHCPv4 component will use Dhcp4 object to configure itself
   and the Logging object to configure logging parameters; it will ignore the
   Dhcp6 object.

   For example, a very simple configuration for both DHCPv4 and DHCPv6 could
   look like this:

 # The whole configuration starts here.
 {

 # DHCPv4 specific configuration starts here.
 "Dhcp4": {
     "interfaces-config": {
         "interfaces": [ "eth0" ],
         "dhcp-socket-type": "raw"
     },
     "valid-lifetime": 4000,
     "renew-timer": 1000,
     "rebind-timer": 2000,
     "subnet4": [{
        "pools": [ { "pool": "192.0.2.1-192.0.2.200" } ],
        "subnet": "192.0.2.0/24"
     }],
     ...
 },
 # DHCPv4 specific configuration ends here.

 # DHCPv6 specific configuration starts here.
 "Dhcp6": {
     "interfaces-config": {
         "interfaces": [ "eth1" ]
     },
     "preferred-lifetime": 3000,
     "valid-lifetime": 4000,
     "renew-timer": 1000,
     "rebind-timer": 2000,
     "subnet6": [{
        "pools": [ { "pool": "2001:db8::/80" } ],
        "subnet": "2001:db8::/64"
     }],
     ...
 },
 # DHCPv6 specific configuration ends here.

 # Logger parameters (that could be shared among several components) start here.
 # This section is used by both the DHCPv4 and DHCPv6 servers.
 "Logging": {
    "loggers": [{
         "name": "*",
         "severity": "DEBUG"
     }],
     ...
 }
 # Logger parameters end here.

 # The whole configuration structure ends here.
 }

   More examples are available in the installed share/doc/kea/examples
   directory.

   To avoid repetition of mostly similar structures, examples in the rest of
   this guide will showcase only the subset of parameters appropriate for a
   given context. For example, when discussing the IPv6 subnets configuration
   in DHCPv6, only subnet6 parameters will be mentioned. It is implied that
   the remaining elements (the global map that holds Dhcp6, Logging and
   possibly DhcpDdns) are present, but they are omitted for clarity. Usually,
   locations where extra parameters may appear are denoted with an ellipsis.

  5.2.2. Simplified Notation

   It is sometimes convenient to refer to a specific element in the
   configuration hierarchy. Each hierarchy level is separated by a slash. If
   there is an array, a specific instance within that array is referenced by
   a number in square brackets (with numbering starting at zero). For
   example, in the above configuration the valid-lifetime in the Dhcp6
   component can be referred to as Dhcp6/valid-lifetime and the pool in the
   first subnet defined in the DHCPv6 configuration as Dhcp6/subnet6[0]/pool.

Chapter 6. Managing Kea with keactrl

   Table of Contents

   6.1. Overview

   6.2. Command Line Options

   6.3. The keactrl Configuration File

   6.4. Commands

   6.5. Overriding the Server Selection

6.1. Overview

   keactrl is a shell script which controls the startup, shutdown and
   reconfiguration of the Kea servers (kea-dhcp4, kea-dhcp6 and
   kea-dhcp-ddns). It also provides the means for checking the current status
   of the servers and determining the configuration files in use.

6.2. Command Line Options

   keactrl is run as follows:

 keactrl <command> [-c keactrl-config-file] [-s server[,server,..]]

   <command> is the one of the commands described in Section 6.4, "Commands".

   The optional -c keactrl-config-file switch allows specification of an
   alternate keactrl configuration file. (--ctrl-config is a synonym for -c.)
   In the absence of -c, keactrl will use the default configuration file
   [kea-install-dir]/etc/kea/keactrl.conf.

   The optional -s server[,server ...] switch selects the servers to which
   the command is issued. (--server is a synonym for -s.) If absent, the
   command is sent to all servers enabled in the keactrl configuration file.
   If multiple servers are specified, they should be separated by commas with
   no intervening spaces.

6.3. The keactrl Configuration File

   Depending on requirements, not all of the available servers need be run.
   The keactrl configuration file sets which servers are enabled and which
   are disabled. The default configuration file is
   [kea-install-dir]/etc/kea/keactrl.conf, but this can be overridden on a
   per-command basis using the -c switch.

   The contents of keactrl.conf are:

 # This is a configuration file for keactrl script which controls
 # the startup, shutdown, reconfiguration and gathering the status
 # of the Kea servers.

 # prefix holds the location where the Kea is installed.
 prefix=/usr/local

 # Location of Kea configuration file.
 kea_config_file=${prefix}/etc/kea/kea.conf

 # Location of Kea binaries.
 exec_prefix=${prefix}
 dhcp4_srv=${exec_prefix}/sbin/kea/kea-dhcp4
 dhcp6_srv=${exec_prefix}/sbin/kea/kea-dhcp6
 dhcp_ddns_srv=${exec_prefix}/sbin/kea/kea-dhcp-ddns

 # Start DHCPv4 server?
 dhcp4=yes

 # Start DHCPv6 server?
 dhcp6=yes

 # Start DHCP DDNS server?
 dhcp_ddns=yes

 # Be verbose?
 kea_verbose=no

   The dhcp4, dhcp6 and dhcp_ddns parameters set to "yes" configure keactrl
   to manage (start, reconfigure) all servers, i.e. kea-dhcp4, kea-dhcp6 and
   kea-dhcp-ddns. When any of these parameters is set to "no" the keactrl
   will ignore the corresponding server when starting or reconfiguring Kea.

   By default, Kea servers managed by keactrl are located in
   [kea-install-dir]/sbin. This should work for most installations. If the
   default location needs to be altered for any reason, the paths specified
   with the dhcp4_srv, dhcp6_srv and dhcp_ddns_srv parameters should be
   modified.

   The kea_verbose parameter specifies the verbosity of the servers being
   started. When kea_verbose is set to "yes" the logging level of the server
   is set to DEBUG. Otherwise, the default logging level is used.

  Note

   The verbosity for the server is set when it is started. Once started, the
   verbosity can be only changed by stopping the server and starting it again
   with the new value of the kea_verbose parameter.

6.4. Commands

   The following commands are supported by keactrl to perform specific
   operations on the Kea servers:

     o start - starts selected servers.
     o stop - stops all running servers.
     o reload - triggers reconfiguration of the selected servers by sending
       the SIGHUP signal to them.
     o status - returns the status of the servers (active or inactive) and
       the names of the configuration files in use.

   Typical output from keactrl when starting the servers looks similar to the
   following:

 $ keactrl start
 INFO/keactrl: Starting kea-dhcp4 -c /usr/local/etc/kea/kea.conf
 INFO/keactrl: Starting kea-dhcp6 -c /usr/local/etc/kea/kea.conf
 INFO/keactrl: Starting kea-dhcp-ddns -c /usr/local/etc/kea/kea.conf

   The following command stops all servers:

 $ keactrl stop
 INFO/keactrl: Skip sending signal 15 to process kea-dhcp6: process is not running

   Note that the stop will attempt to stop all servers regardless of whether
   they are "enabled" in the keactrl.conf. If any of the servers is not
   running, an informational message is displayed as in the stop command
   output above.

   As already mentioned, the reconfiguration of each Kea server is triggered
   by the SIGHUP signal. The reload command sends the SIGHUP signal to the
   servers that are enabled in the keactrl configuration file and are
   currently running. When a server receives the SIGHUP signal it re-reads
   its configuration file and, if the new configuration is valid, uses the
   new configuration. A reload is executed as follows:

 $ keactrl reload

  Note

   Currently keactrl does not report configuration failures when the server
   is started or reconfigured. To check if the server's configuration
   succeeded the Kea log must be examined for errors. By default, this is
   written to the syslog file.

   Sometimes it is useful to check which servers are running. The status
   reports this, typical output looking like:

 $ keactrl status
 DHCPv4 server: active
 DHCPv6 server: inactive
 DHCP DDNS: active
 Kea configuration file: /usr/local/etc/kea/kea.conf
 keactrl configuration file: /usr/local/etc/kea/keactrl.conf

6.5. Overriding the Server Selection

   The optional -s switch allows the selection of the servers to which
   keactrl command is issued. For example, the following instructs keactrl to
   stop the kea-dhcp4 and kea-dhcp6 servers and leave the kea-dhcp-ddns
   server running:

 $ keactrl stop -s dhcp4,dhcp6

   Similarly, the following will only start the kea-dhcp4 and kea-dhcp-ddns
   servers and not kea-dhcp6.

 $ keactrl start -s dhcp4,dhcp_ddns

   Note that the behavior of the -s switch with the start and reload commands
   is different to its behavior with the stop command. On start and reload,
   keactrl will check if the servers given as parameters to the -s switch are
   enabled in the keactrl configuration file: if not, the server will be
   ignored. For stop however, this check is not made: the command is applied
   to all listed servers, regardless of whether they have been enabled in the
   file.

   The following keywords can be used with the -s command line option:

     o dhcp4 for kea-dhcp4.
     o dhcp6 for kea-dhcp6.
     o dhcp_ddns for kea-dhcp-ddns.
     o all for all servers (default).

Chapter 7. The DHCPv4 Server

   Table of Contents

   7.1. Starting and Stopping the DHCPv4 Server

   7.2. DHCPv4 Server Configuration

                7.2.1. Introduction

                7.2.2. Lease Storage

                7.2.3. Interface configuration

                7.2.4. IPv4 Subnet Identifier

                7.2.5. Configuration of IPv4 Address Pools

                7.2.6. Standard DHCPv4 options

                7.2.7. Custom DHCPv4 options

                7.2.8. DHCPv4 Vendor Specific Options

                7.2.9. Nested DHCPv4 Options (Custom Option Spaces)

                7.2.10. Unspecified parameters for DHCPv4 option
                configuration

                7.2.11. Stateless Configuration of DHCPv4 clients

                7.2.12. Client Classification in DHCPv4

                7.2.13. Configuring DHCPv4 for DDNS

                7.2.14. Next Server (siaddr)

                7.2.15. Echoing Client-ID (RFC 6842)

   7.3. Host reservation in DHCPv4

                7.3.1. Address reservation types

                7.3.2. Conflicts in DHCPv4 reservations

                7.3.3. Reserving a hostname

                7.3.4. Reserving specific options

                7.3.5. Fine Tuning IPv4 Host Reservation

   7.4. Server Identifier in DHCPv4

   7.5. How the DHCPv4 Server Selects a Subnet for the Client

                7.5.1. Using a Specific Relay Agent for a Subnet

                7.5.2. Segregating IPv4 Clients in a Cable Network

   7.6. Supported DHCP Standards

   7.7. DHCPv4 Server Limitations

7.1. Starting and Stopping the DHCPv4 Server

   It is recommended that the Kea DHCPv4 server be started and stopped using
   keactrl (described in Chapter 6, Managing Kea with keactrl). However, it
   is also possible to run the server directly: it accepts the following
   command-line switches:

     o -c file - specifies the configuration file. This is the only mandatory
       switch.
     o -d - specifies whether the server logging should be switched to
       debug/verbose mode. In verbose mode, the logging severity and
       debuglevel specified in the configuration file are ignored and "debug"
       severity and the maximum debuglevel (99) are assumed. The flag is
       convenient, for temporarily switching the server into maximum
       verbosity, e.g. when debugging.
     o -p port - specifies UDP port the server will listen on. This is only
       useful during testing, as the DHCPv4 server listening on ports other
       than default DHCPv4 ports will not be able to handle regular DHCPv4
       queries.
     o -v - prints out Kea version and exits.
     o -V - prints out Kea extended version with additional parameters and
       exits.

   When running in a console, the server can be shut down by pressing ctrl-c.
   It detects the key combination and shuts down gracefully.

   On start-up, the server will detect available network interfaces and will
   attempt to open UDP sockets on all interfaces mentioned in the
   configuration file.

   Since the DHCPv4 server opens privileged ports, it requires root access.
   Make sure you run this daemon as root.

7.2. DHCPv4 Server Configuration

  7.2.1. Introduction

   This section explains how to configure the DHCPv4 server using the Kea
   configuration backend. (Kea configuration using any other backends is
   outside of scope of this document.) Before DHCPv4 is started, its
   configuration file has to be created. The basic configuration is as
   follows:

 {
 # DHCPv4 configuration starts in this line
 "Dhcp4": {

 # First we set up global values
     "valid-lifetime": 4000,
     "renew-timer": 1000,
     "rebind-timer": 2000,

 # Next we setup the interfaces to be used by the server.
     "interfaces-config": {
         "interfaces": [ "eth0" ]
     },

 # And we specify the type of lease database
     "lease-database": {
         "type": "memfile",
         "persist": true,
         "name": "/var/kea/dhcp4.leases"
     },

 # Finally, we list the subnets from which we will be leasing addresses.
     "subnet4": [
         {
             "subnet": "192.0.2.0/24",
             "pools": [
                 { "pool": "192.0.2.1 - 192.0.2.200" }
             ]
         }
     ]

 # DHCPv4 configuration ends with this line
 }

 }

   The following paragraphs provide a brief overview of the parameters in the
   above example and their format. Subsequent sections of this chapter go
   into much greater detail for these and other parameters.

   The lines starting with a hash (#) are comments and are ignored by the
   server; they do not impact its operation in any way.

   The configuration starts in the first line with the initial opening curly
   bracket (or brace). Each configuration consists of one or more objects. In
   this specific example, we have only one object called Dhcp4. This is a
   simplified configuration, as usually there will be additional objects,
   like Logging or DhcpDns, but we omit them now for clarity. The Dhcp4
   configuration starts with the "Dhcp4": { line and ends with the
   corresponding closing brace (in the above example, the brace after the
   last comment). Everything defined between those lines is considered to be
   the Dhcp4 configuration.

   In the general case, the order in which those parameters appear does not
   matter. There are two caveats here though. The first one is to remember
   that the configuration file must be well formed JSON. That means that the
   parameters for any given scope must be separated by a comma and there must
   not be a comma after the last parameter. When reordering a configuration
   file, keep in mind that moving a parameter to or from the last position in
   a given scope may also require moving the comma. The second caveat is that
   it is uncommon -- although legal JSON -- to repeat the same parameter
   multiple times. If that happens, the last occurrence of a given parameter
   in a given scope is used while all previous instances are ignored. This is
   unlikely to cause any confusion as there are no real life reasons to keep
   multiple copies of the same parameter in your configuration file.

   Moving onto the DHCPv4 configuration elements, the very first few elements
   define some global parameters. valid-lifetime defines for how long the
   addresses (leases) given out by the server are valid. If nothing changes,
   a client that got an address is allowed to use it for 4000 seconds. (Note
   that integer numbers are specified as is, without any quotes around them.)
   renew-timer and rebind-timer are values that define T1 and T2 timers that
   govern when the client will begin the renewal and rebind procedures. Note
   that renew-timer and rebind-timer are optional. If they are not specified
   the client will select values for T1 and T2 timers according to the RFC
   2131.

   The interfaces-config map specifies the server configuration concerning
   the network interfaces, on which the server should listen to the DHCP
   messages. The interfaces parameter specifies a list of network interfaces
   on which the server should listen. Lists are opened and closed with square
   brackets, with elements separated by commas. Had we wanted to listen on
   two interfaces, the interfaces-config would look like this:

 "interfaces-config": {
     "interfaces": [ "eth0", "eth1" ]
 },

   The next couple of lines define the lease database, the place where the
   server stores its lease information. This particular example tells the
   server to use memfile, which is the simplest (and fastest) database
   backend. It uses an in-memory database and stores leases on disk in a CSV
   file. This is a very simple configuration. Usually, lease database
   configuration is more extensive and contains additional parameters. Note
   that lease-database is an object and opens up a new scope, using an
   opening brace. Its parameters (just one in this example -- type) follow.
   Had there been more than one, they would be separated by commas. This
   scope is closed with a closing brace. As more parameters follow, a
   trailing comma is present.

   Finally, we need to define a list of IPv4 subnets. This is the most
   important DHCPv4 configuration structure as the server uses that
   information to process clients' requests. It defines all subnets from
   which the server is expected to receive DHCP requests. The subnets are
   specified with the subnet4 parameter. It is a list, so it starts and ends
   with square brackets. Each subnet definition in the list has several
   attributes associated with it, so it is a structure and is opened and
   closed with braces. At a minimum, a subnet definition has to have at least
   two parameters: subnet (that defines the whole subnet) and pools (which is
   a list of dynamically allocated pools that are governed by the DHCP
   server).

   The example contains a single subnet. Had more than one been defined,
   additional elements in the subnet4 parameter would be specified and
   separated by commas. For example, to define three subnets, the following
   syntax would be used:

 "subnet4": [
     {
         "pools": [ { "pool":  "192.0.2.1 - 192.0.2.200" } ],
         "subnet": "192.0.2.0/24"
     },
     {
         "pools": [ { "pool": "192.0.3.100 - 192.0.3.200" } ],
         "subnet": "192.0.3.0/24"
     },
     {
         "pools": [ { "pool": "192.0.4.1 - 192.0.4.254" } ],
         "subnet": "192.0.4.0/24"
     }
 ]

   After all parameters are specified, we have two contexts open: global and
   Dhcp4, hence we need two closing curly brackets to close them. In a real
   life configuration file there most likely would be additional components
   defined such as Logging or DhcpDdns, so the closing brace would be
   followed by a comma and another object definition.

  7.2.2. Lease Storage

   All leases issued by the server are stored in the lease database.
   Currently there are three database backends available: memfile (which is
   the default backend), MySQL and PostgreSQL.

    7.2.2.1. Memfile, Basic Storage for Leases

   The server is able to store lease data in different repositories. Larger
   deployments may elect to store leases in a database. Section 7.2.2.2,
   "Database Configuration" describes this option. In typical smaller
   deployments though, the server will use a CSV file rather than a database
   to store lease information. As well as requiring less administration, an
   advantage of using a file for storage is that it eliminates a dependency
   on third-party database software.

   The configuration of the file backend (Memfile) is controlled through the
   Dhcp4/lease-database parameters. The type parameter is mandatory and it
   specifies which storage for leases the server should use. The value of
   "memfile" indicates that the file should be used as the storage. The
   following list presents the remaining, not mandatory parameters, which can
   be used to configure the Memfile backend.

     o persist: controls whether the new leases and updates to existing
       leases are written to the file. It is strongly recommended that the
       value of this parameter is set to true at all times, during the
       server's normal operation. Not writing leases to disk will mean that
       if a server is restarted (e.g. after a power failure), it will not
       know what addresses have been assigned. As a result, it may hand out
       addresses to new clients that are already in use. The value of false
       is mostly useful for performance testing purposes. The default value
       of the persist parameter is true, which enables writing lease updates
       to the lease file.
     o name: specifies an absolute location of the lease file in which new
       leases and lease updates will be recorded. The default value for this
       parameter is "[kea-install-dir]/var/kea/kea-leases4.csv" .
     o lfc-interval: specifies the interval in seconds, at which the server
       (Memfile backend) will perform a lease file cleanup (LFC), which
       removes the redundant (historical) information from the lease file and
       effectively reduces the lease file size. The cleanup process is
       described in more detailed fashion further in this section. The
       default value of the lfc-interval is 0, which disables the LFC.

   The example configuration of the Memfile backend is presented below:

 "Dhcp4": {
     "lease-database": {
         "type": "memfile",
         "persist": true,
         "name": "/tmp/kea-leases4.csv",
         "lfc-interval": 1800
     }
 }

   This configuration selects the /tmp/kea-leases4.csv as the storage for
   lease information and enables persistence (writing lease updates to this
   file). It also configures the backend perform the periodic cleanup of the
   lease files, executed every 30 minutes.

   It is important to know how the lease file contents are organized to
   understand why the periodic lease file cleanup is needed. Every time when
   the server updates a lease or creates a new lease for the client, the new
   lease information must be recorded in the lease file. For performance
   reasons, the server does not supersede the existing client's lease, as it
   would require the lookup of the specific lease entry, but simply appends
   the new lease information at the end of the lease file. The previous lease
   entries for the client are not removed. When the server loads leases from
   the lease file, e.g. at the server startup, it assumes that the latest
   lease entry for the client is the valid one. The previous entries are
   discarded. This means that the server can re-construct the accurate
   information about the leases even though there may be many lease entries
   for each client. However, storing many entries for each client results in
   bloated lease file and impairs the performance of the server's startup and
   reconfiguration, as it needs to process larger number of lease entries.

   The lease file cleanup removes all previous entries for each client and
   leaves only the latest ones. The interval at which the cleanup is
   performed is configurable, and it should be selected according to the
   frequency of lease renewals initiated by the clients. The more frequent
   renewals are, the lesser value of the lfc-interval should be. Note
   however, that the LFC takes time and thus it is possible (although
   unlikely) that new cleanup is started while the previous cleanup instance
   is still running, if the lfc-interval is too short. The server would
   recover from this by skipping the new cleanup when it detects that the
   previous cleanup is still in progress. But, this implies that the actual
   cleanups will be triggered more rarely than configured. Moreover,
   triggering a new cleanup adds an overhead to the server, which will not be
   able to respond to new requests for a short period of time when the new
   cleanup process is spawned. Therefore, it is recommended that the
   lfc-interval value is selected in a way that would allow for completing
   the cleanup before the new cleanup is triggered.

   The LFC is performed by a separate process (in background) to avoid
   performance impact on the server process. In order to avoid the conflicts
   between the two processes both using the same lease files, the LFC process
   operates on the copy of the original lease file, rather than on the lease
   file used by the server to record lease updates. There are also other
   files being created as a side effect of the lease file cleanup. The
   detailed description of the LFC is located on the Kea wiki:
   http://kea.isc.org/wiki/LFCDesign.

    7.2.2.2. Database Configuration

  Note

   Database access information must be configured for the DHCPv4 server, even
   if it has already been configured for the DHCPv6 server. The servers store
   their information independently, so each server can use a separate
   database or both servers can use the same database.

   Database configuration is controlled through the Dhcp4/lease-database
   parameters. The type of the database must be set to "mysql" or
   "postgresql", e.g.

 "Dhcp4": { "lease-database": { "type": "mysql", ... }, ... }

   Next, the name of the database to hold the leases must be set: this is the
   name used when the lease database was created (see Section 4.3.2.1, "First
   Time Creation of Kea Database" or Section 4.3.3.1, "Manually Create the
   PostgreSQL Database and the Kea User").

 "Dhcp4": { "lease-database": { "name": "database-name" , ... }, ... }

   If the database is located on a different system to the DHCPv4 server, the
   database host name must also be specified (although it should be noted
   that this configuration may have a severe impact on server performance):

 "Dhcp4": { "lease-database": { "host": remote-host-name, ... }, ... }

   The usual state of affairs will be to have the database on the same
   machine as the DHCPv4 server. In this case, set the value to the empty
   string:

 "Dhcp4": { "lease-database": { "host" : "", ... }, ... }

   Finally, the credentials of the account under which the server will access
   the database should be set:

 "Dhcp4": { "lease-database": { "user": "user-name",
                                "password": "password",
                               ... },
            ... }

   If there is no password to the account, set the password to the empty
   string "". (This is also the default.)

  7.2.3. Interface configuration

   The DHCPv4 server has to be configured to listen on specific network
   interfaces. The simplest network interface configuration tells the server
   to listen on all available interfaces:

 "Dhcp4": {
     "interfaces-config": {
         "interfaces": [ "*" ]
     }
     ...
 },


   The asterisk plays the role of a wildcard and means "listen on all
   interfaces". However, it is usually a good idea to explicitly specify
   interface names:

 "Dhcp4": {
     "interfaces-config": {
         "interfaces": [ "eth1", "eth3" ]
     },
     ...
 }


   It is possible to use wildcard interface name (asterisk) concurrently with
   explicit interface names:

 "Dhcp4": {
     "interfaces-config": {
         "interfaces": [ "eth1", "eth3", "*" ]
     },
     ...
 }


   It is anticipated that this form of usage will only be used when it is
   desired to temporarily override a list of interface names and listen on
   all interfaces.

   Some deployments of the DHCP servers require that the servers listen on
   the interfaces with multiple IPv4 addresses configured. In these
   situations, the address to use can be selected by appending an IPv4
   address to the interface name in the following manner:

 "Dhcp4": {
     "interfaces-config": {
         "interfaces": [ "eth1/10.0.0.1", "eth3/192.0.2.3" ]
     },
     ...
 }


   If it is desired that the server listens on multiple IPv4 addresses
   assigned to the same interface, multiple addresses can be specified for
   this interface as in the example below:

 "Dhcp4": {
     "interfaces-config": {
         "interfaces": [ "eth1/10.0.0.1", "eth1/10.0.0.2" ]
     },
     ...
 }


   Alternatively, if the server should listen on all addresses for the
   particular interface, an interface name without any address should be
   specified.

   Kea supports responding to directly connected clients which don't have an
   address configured on the interface yet. This requires that the server
   injects the hardware address of the destination into the data link layer
   of the packet being sent to the client. The DHCPv4 server utilizes the raw
   sockets to achieve this, and builds the entire IP/UDP stack for the
   outgoing packets. The down side of raw socket use, however, is that
   incoming and outgoing packets bypass the firewalls (e.g. iptables). It is
   also troublesome to handle traffic on multiple IPv4 addresses assigned to
   the same interface, as raw sockets are bound to the interface and advanced
   packet filtering techniques (e.g. using the BPF) have to be used to
   receive unicast traffic on the desired addresses assigned to the
   interface, rather than capturing whole traffic reaching the interface to
   which the raw socket is bound. Therefore, in the deployments where the
   server doesn't have to provision the directly connected clients and only
   receives the unicast packets from the relay agents, it is desired to
   configure the DHCP server to utilize the IP/UDP datagram sockets, instead
   of raw sockets. The following configuration demonstrates how this can be
   achieved:

 "Dhcp4": {
     "interfaces-config": {
         "interfaces": [ "eth1", "eth3" ],
         "dhcp-socket-type": "udp"
     },
     ...
 }


   The dhcp-socket-type specifies that the IP/UDP sockets will be opened on
   all interfaces on which the server listens, i.e. "eth1" and "eth3" in our
   case. If the dhcp-socket-type is set to raw, it configures the server to
   use raw sockets instead. If the dhcp-socket-type value is not specified,
   the default value raw is used.

   Using UDP sockets automatically disables the reception of brodcast packets
   from directly connected clients. This effectively means that the UDP
   sockets can be used for relayed traffic only. When using the raw sockets,
   both the traffic from the directly connected clients and the relayed
   traffic will be handled. Caution should be taken when configuring the
   server to open multiple raw sockets on the interface with several IPv4
   addresses assigned. If the directly connected client sends the message to
   the brodcast address all sockets on this link will receive this message
   and multiple responses will be sent to the client. Hence, the
   configuration with multiple IPv4 addresses assigned to the interface
   should not be used when the directly connected clients are operating on
   that link. To use a single address on such interface, the
   "interface-name/address" notation should be used.

  Note

   Specifying the value raw as the socket type, doesn't guarantee that the
   raw sockets will be used! The use of raw sockets to handle the traffic
   from the directly connected clients is currently supported on Linux and
   BSD systems only. If the raw sockets are not supported on the particular
   OS, the server will issue a warning and fall back to use the IP/UDP
   sockets.

  7.2.4. IPv4 Subnet Identifier

   The subnet identifier is a unique number associated with a particular
   subnet. In principle, it is used to associate clients' leases with their
   respective subnets. When a subnet identifier is not specified for a subnet
   being configured, it will be automatically assigned by the configuration
   mechanism. The identifiers are assigned from 1 and are monotonically
   increased for each subsequent subnet: 1, 2, 3 ....

   If there are multiple subnets configured with auto-generated identifiers
   and one of them is removed, the subnet identifiers may be renumbered. For
   example: if there are four subnets and the third is removed the last
   subnet will be assigned the identifier that the third subnet had before
   removal. As a result, the leases stored in the lease database for subnet 3
   are now associated with subnet 4, something that may have unexpected
   consequences. It is planned to implement a mechanism to preserve
   auto-generated subnet ids in a future version of Kea. However, the only
   remedy for this issue at present is to manually specify a unique
   identifier for each subnet.

   The following configuration will assign the specified subnet identifier to
   the newly configured subnet:

 "Dhcp4": {
     "subnet4": [
         {
             "subnet": "192.0.2.0/24",
             "id": 1024,
             ...
         }
     ]
 }

   This identifier will not change for this subnet unless the "id" parameter
   is removed or set to 0. The value of 0 forces auto-generation of the
   subnet identifier.

  7.2.5. Configuration of IPv4 Address Pools

   The essential role of DHCPv4 server is address assignment. The server has
   to be configured with at least one subnet and one pool of dynamic
   addresses to be managed. For example, assume that the server is connected
   to a network segment that uses the 192.0.2.0/24 prefix. The Administrator
   of that network has decided that addresses from range 192.0.2.10 to
   192.0.2.20 are going to be managed by the Dhcp4 server. Such a
   configuration can be achieved in the following way:

 "Dhcp4": {
     "subnet4": [
         {
             "subnet": "192.0.2.0/24",
             "pools": [
                 { "pool": "192.0.2.10 - 192.0.2.20" }
             ],
             ...
         }
     ]
 }

   Note that subnet is defined as a simple string, but the pools parameter is
   actually a list of pools: for this reason, the pools definition is
   enclosed in square brackets, even though only one range of addresses is
   specified in this example.

   Each pool is a structure that contains the parameters that describe a
   single pool. Currently there is only one parameter, pool, which gives the
   range of addresses in the pool. Additional parameters will be added in
   future releases of Kea.

   It is possible to define more than one pool in a subnet: continuing the
   previous example, further assume that 192.0.2.64/26 should be also be
   managed by the server. It could be written as 192.0.2.64 to 192.0.2.127.
   Alternatively, it can be expressed more simply as 192.0.2.64/26. Both
   formats are supported by Dhcp4 and can be mixed in the pool list. For
   example, one could define the following pools:

 "Dhcp4": {
     "subnet4": [
         {
             "subnet": "192.0.2.0/24",
             "pools": [
                 { "pool": "192.0.2.10-192.0.2.20" },
                 { "pool": "192.0.2.64/26" }
             ],
             ...
         }
     ],
     ...
 }

   The number of pools is not limited, but for performance reasons it is
   recommended to use as few as possible. White space in pool definitions is
   ignored, so spaces before and after the hyphen are optional. They can be
   used to improve readability.

   The server may be configured to serve more than one subnet:

 "Dhcp4": {
     "subnet4": [
         {
             "subnet": "192.0.2.0/24",
             "pools": [ { "pool": "192.0.2.1 - 192.0.2.200" } ],
             ...
         },
         {
             "subnet": "192.0.3.0/24",
             "pools": [ { "pool": "192.0.3.100 - 192.0.3.200" } ],
             ...
         },
         {
             "subnet": "192.0.4.0/24",
             "pools": [ { "pool": "192.0.4.1 - 192.0.4.254" } ],
             ...
         }
     ]
 }

   When configuring a DHCPv4 server using prefix/length notation, please pay
   attention to the boundary values. When specifying that the server can use
   a given pool, it will also be able to allocate the first (typically
   network address) and the last (typically broadcast address) address from
   that pool. In the aforementioned example of pool 192.0.3.0/24, both
   192.0.3.0 and 192.0.3.255 addresses may be assigned as well. This may be
   invalid in some network configurations. If you want to avoid this, please
   use the "min-max" notation.

  7.2.6. Standard DHCPv4 options

   One of the major features of the DHCPv4 server is to provide configuration
   options to clients. Although there are several options that require
   special behavior, most options are sent by the server only if the client
   explicitly requests them. The following example shows how to configure the
   addresses of DNS servers, which is one of the most frequently used
   options. Options specified in this way are considered global and apply to
   all configured subnets.

 "Dhcp4": {
     "option-data": [
         {
            "name": "domain-name-servers",
            "code": 6,
            "space": "dhcp4",
            "csv-format": true,
            "data": "192.0.2.1, 192.0.2.2"
         },
         ...
     ]
 }

   The name parameter specifies the option name. For a complete list of
   currently supported names, see Table 7.1, "List of standard DHCPv4
   options" below. The code parameter specifies the option code, which must
   match one of the values from that list. The next line specifies the option
   space, which must always be set to "dhcp4" as these are standard DHCPv4
   options. For other option spaces, including custom option spaces, see
   Section 7.2.9, "Nested DHCPv4 Options (Custom Option Spaces)". The next
   line specifies the format in which the data will be entered: use of CSV
   (comma separated values) is recommended. The sixth line gives the actual
   value to be sent to clients. Data is specified as normal text, with values
   separated by commas if more than one value is allowed.

   Options can also be configured as hexadecimal values. If csv-format is set
   to false, option data must be specified as a hexadecimal string. The
   following commands configure the domain-name-servers option for all
   subnets with the following addresses: 192.0.3.1 and 192.0.3.2. Note that
   csv-format is set to false.

 "Dhcp4": {
     "option-data": [
         {
             "name": "domain-name-servers",
             "code": 6,
             "space": "dhcp4",
             "csv-format": false,
             "data": "C0 00 03 01 C0 00 03 02"
         },
         ...
     ],
     ...
 }

   Most of the parameters in the "option-data" structure are optional and can
   be omitted in some circumstances as discussed in the Section 7.2.10,
   "Unspecified parameters for DHCPv4 option configuration".

   It is possible to specify or override options on a per-subnet basis. If
   clients connected to most of your subnets are expected to get the same
   values of a given option, you should use global options: you can then
   override specific values for a small number of subnets. On the other hand,
   if you use different values in each subnet, it does not make sense to
   specify global option values (Dhcp4/option-data), rather you should set
   only subnet-specific values (Dhcp4/subnet[X]/option-data[Y]).

   The following commands override the global DNS servers option for a
   particular subnet, setting a single DNS server with address 192.0.2.3.

 "Dhcp4": {
     "subnet4": [
         {
             "option-data": [
                 {
                     "name": "domain-name-servers",
                     "code": 6,
                     "space": "dhcp4",
                     "csv-format": true,
                     "data": "192.0.2.3"
                 },
                 ...
             ],
             ...
         },
         ...
     ],
     ...
 }

   The currently supported standard DHCPv4 options are listed in Table 7.1,
   "List of standard DHCPv4 options" and Table 7.2, "List of standard DHCPv4
   options (continued)". The "Name" and "Code" are the values that should be
   used as a name in the option-data structures. "Type" designates the format
   of the data: the meanings of the various types is given in Table 7.3,
   "List of standard DHCP option types".

   Some options are designated as arrays, which means that more than one
   value is allowed in such an option. For example the option time-servers
   allows the specification of more than one IPv4 address, so allowing
   clients to obtain the addresses of multiple NTP servers.

   The Section 7.2.7, "Custom DHCPv4 options" describes the configuration
   syntax to create custom option definitions (formats). It is generally not
   allowed to create custom definitions for standard options, even if the
   definition being created matches the actual option format defined in the
   RFCs. There is an exception from this rule for standard options for which
   Kea does not provide a definition yet. In order to use such options, a
   server administrator must create a definition as described in
   Section 7.2.7, "Custom DHCPv4 options" in the 'dhcp4' option space. This
   definition should match the option format described in the relevant RFC
   but the configuration mechanism will allow any option format as it has no
   means to validate the format at the moment.

   Table 7.1. List of standard DHCPv4 options

   +------------------------------------------------------------+
   |            Name             | Code |     Type     | Array? |
   |-----------------------------+------+--------------+--------|
   | subnet-mask                 |  1   | ipv4-address | false  |
   |-----------------------------+------+--------------+--------|
   | time-offset                 |  2   |    int32     | false  |
   |-----------------------------+------+--------------+--------|
   | routers                     |  3   | ipv4-address |  true  |
   |-----------------------------+------+--------------+--------|
   | time-servers                |  4   | ipv4-address |  true  |
   |-----------------------------+------+--------------+--------|
   | name-servers                |  5   | ipv4-address | false  |
   |-----------------------------+------+--------------+--------|
   | domain-name-servers         |  6   | ipv4-address |  true  |
   |-----------------------------+------+--------------+--------|
   | log-servers                 |  7   | ipv4-address |  true  |
   |-----------------------------+------+--------------+--------|
   | cookie-servers              |  8   | ipv4-address |  true  |
   |-----------------------------+------+--------------+--------|
   | lpr-servers                 |  9   | ipv4-address |  true  |
   |-----------------------------+------+--------------+--------|
   | impress-servers             |  10  | ipv4-address |  true  |
   |-----------------------------+------+--------------+--------|
   | resource-location-servers   |  11  | ipv4-address |  true  |
   |-----------------------------+------+--------------+--------|
   | host-name                   |  12  |    string    | false  |
   |-----------------------------+------+--------------+--------|
   | boot-size                   |  13  |    uint16    | false  |
   |-----------------------------+------+--------------+--------|
   | merit-dump                  |  14  |    string    | false  |
   |-----------------------------+------+--------------+--------|
   | domain-name                 |  15  |     fqdn     | false  |
   |-----------------------------+------+--------------+--------|
   | swap-server                 |  16  | ipv4-address | false  |
   |-----------------------------+------+--------------+--------|
   | root-path                   |  17  |    string    | false  |
   |-----------------------------+------+--------------+--------|
   | extensions-path             |  18  |    string    | false  |
   |-----------------------------+------+--------------+--------|
   | ip-forwarding               |  19  |   boolean    | false  |
   |-----------------------------+------+--------------+--------|
   | non-local-source-routing    |  20  |   boolean    | false  |
   |-----------------------------+------+--------------+--------|
   | policy-filter               |  21  | ipv4-address |  true  |
   |-----------------------------+------+--------------+--------|
   | max-dgram-reassembly        |  22  |    uint16    | false  |
   |-----------------------------+------+--------------+--------|
   | default-ip-ttl              |  23  |    uint8     | false  |
   |-----------------------------+------+--------------+--------|
   | path-mtu-aging-timeout      |  24  |    uint32    | false  |
   |-----------------------------+------+--------------+--------|
   | path-mtu-plateau-table      |  25  |    uint16    |  true  |
   |-----------------------------+------+--------------+--------|
   | interface-mtu               |  26  |    uint16    | false  |
   |-----------------------------+------+--------------+--------|
   | all-subnets-local           |  27  |   boolean    | false  |
   |-----------------------------+------+--------------+--------|
   | broadcast-address           |  28  | ipv4-address | false  |
   |-----------------------------+------+--------------+--------|
   | perform-mask-discovery      |  29  |   boolean    | false  |
   |-----------------------------+------+--------------+--------|
   | mask-supplier               |  30  |   boolean    | false  |
   |-----------------------------+------+--------------+--------|
   | router-discovery            |  31  |   boolean    | false  |
   |-----------------------------+------+--------------+--------|
   | router-solicitation-address |  32  | ipv4-address | false  |
   |-----------------------------+------+--------------+--------|
   | static-routes               |  33  | ipv4-address |  true  |
   |-----------------------------+------+--------------+--------|
   | trailer-encapsulation       |  34  |   boolean    | false  |
   |-----------------------------+------+--------------+--------|
   | arp-cache-timeout           |  35  |    uint32    | false  |
   |-----------------------------+------+--------------+--------|
   | ieee802-3-encapsulation     |  36  |   boolean    | false  |
   |-----------------------------+------+--------------+--------|
   | default-tcp-ttl             |  37  |    uint8     | false  |
   |-----------------------------+------+--------------+--------|
   | tcp-keepalive-interval      |  38  |    uint32    | false  |
   |-----------------------------+------+--------------+--------|
   | tcp-keepalive-garbage       |  39  |   boolean    | false  |
   +------------------------------------------------------------+

   Table 7.2. List of standard DHCPv4 options (continued)

   +-------------------------------------------------------------+
   |             Name             | Code |     Type     | Array? |
   |------------------------------+------+--------------+--------|
   | nis-domain                   | 40   | string       | false  |
   |------------------------------+------+--------------+--------|
   | nis-servers                  | 41   | ipv4-address | true   |
   |------------------------------+------+--------------+--------|
   | ntp-servers                  | 42   | ipv4-address | true   |
   |------------------------------+------+--------------+--------|
   | vendor-encapsulated-options  | 43   | empty        | false  |
   |------------------------------+------+--------------+--------|
   | netbios-name-servers         | 44   | ipv4-address | true   |
   |------------------------------+------+--------------+--------|
   | netbios-dd-server            | 45   | ipv4-address | true   |
   |------------------------------+------+--------------+--------|
   | netbios-node-type            | 46   | uint8        | false  |
   |------------------------------+------+--------------+--------|
   | netbios-scope                | 47   | string       | false  |
   |------------------------------+------+--------------+--------|
   | font-servers                 | 48   | ipv4-address | true   |
   |------------------------------+------+--------------+--------|
   | x-display-manager            | 49   | ipv4-address | true   |
   |------------------------------+------+--------------+--------|
   | dhcp-requested-address       | 50   | ipv4-address | false  |
   |------------------------------+------+--------------+--------|
   | dhcp-option-overload         | 52   | uint8        | false  |
   |------------------------------+------+--------------+--------|
   | dhcp-message                 | 56   | string       | false  |
   |------------------------------+------+--------------+--------|
   | dhcp-max-message-size        | 57   | uint16       | false  |
   |------------------------------+------+--------------+--------|
   | vendor-class-identifier      | 60   | binary       | false  |
   |------------------------------+------+--------------+--------|
   | nwip-domain-name             | 62   | string       | false  |
   |------------------------------+------+--------------+--------|
   | nwip-suboptions              | 63   | binary       | false  |
   |------------------------------+------+--------------+--------|
   | tftp-server-name             | 66   | string       | false  |
   |------------------------------+------+--------------+--------|
   | boot-file-name               | 67   | string       | false  |
   |------------------------------+------+--------------+--------|
   | user-class                   | 77   | binary       | false  |
   |------------------------------+------+--------------+--------|
   | fqdn                         | 81   | record       | false  |
   |------------------------------+------+--------------+--------|
   | dhcp-agent-options           | 82   | empty        | false  |
   |------------------------------+------+--------------+--------|
   | authenticate                 | 90   | binary       | false  |
   |------------------------------+------+--------------+--------|
   | client-last-transaction-time | 91   | uint32       | false  |
   |------------------------------+------+--------------+--------|
   | associated-ip                | 92   | ipv4-address | true   |
   |------------------------------+------+--------------+--------|
   | subnet-selection             | 118  | ipv4-address | false  |
   |------------------------------+------+--------------+--------|
   | domain-search                | 119  | binary       | false  |
   |------------------------------+------+--------------+--------|
   | vivco-suboptions             | 124  | binary       | false  |
   |------------------------------+------+--------------+--------|
   | vivso-suboptions             | 125  | binary       | false  |
   +-------------------------------------------------------------+

   Table 7.3. List of standard DHCP option types

   +------------------------------------------------------------------------+
   |     Name     |                         Meaning                         |
   |--------------+---------------------------------------------------------|
   | binary       | An arbitrary string of bytes, specified as a set of     |
   |              | hexadecimal digits.                                     |
   |--------------+---------------------------------------------------------|
   | boolean      | Boolean value with allowed values true or false         |
   |--------------+---------------------------------------------------------|
   | empty        | No value, data is carried in suboptions                 |
   |--------------+---------------------------------------------------------|
   | fqdn         | Fully qualified domain name (e.g. www.example.com)      |
   |--------------+---------------------------------------------------------|
   | ipv4-address | IPv4 address in the usual dotted-decimal notation (e.g. |
   |              | 192.0.2.1)                                              |
   |--------------+---------------------------------------------------------|
   | ipv6-address | IPv6 address in the usual colon notation (e.g.          |
   |              | 2001:db8::1)                                            |
   |--------------+---------------------------------------------------------|
   | record       | Structured data that may comprise any types (except     |
   |              | "record" and "empty")                                   |
   |--------------+---------------------------------------------------------|
   | string       | Any text                                                |
   |--------------+---------------------------------------------------------|
   | uint8        | 8 bit unsigned integer with allowed values 0 to 255     |
   |--------------+---------------------------------------------------------|
   | uint16       | 16 bit unsigned integer with allowed values 0 to 65535  |
   |--------------+---------------------------------------------------------|
   | uint32       | 32 bit unsigned integer with allowed values 0 to        |
   |              | 4294967295                                              |
   +------------------------------------------------------------------------+

  7.2.7. Custom DHCPv4 options

   Kea supports custom (non-standard) DHCPv4 options. Assume that we want to
   define a new DHCPv4 option called "foo" which will have code 222 and will
   convey a single unsigned 32 bit integer value. We can define such an
   option by using the following entry in the configuration file:

 "Dhcp4": {
     "option-def": [
         {
             "name": "foo",
             "code": 222,
             "type": "uint32",
             "array": false,
             "record-types": "",
             "space": "dhcp4",
             "encapsulate": ""
         }, ...
     ],
     ...
 }

   The false value of the array parameter determines that the option does NOT
   comprise an array of "uint32" values but rather a single value. Two other
   parameters have been left blank: record-types and encapsulate. The former
   specifies the comma separated list of option data fields if the option
   comprises a record of data fields. This should be non-empty if the type is
   set to "record". Otherwise it must be left blank. The latter parameter
   specifies the name of the option space being encapsulated by the
   particular option. If the particular option does not encapsulate any
   option space it should be left blank. Note that the above set of comments
   define the format of the new option and do not set its values.

  Note

   In the current release the default values are not propagated to the parser
   when the new configuration is being set. Therefore, all parameters must be
   specified at all times, even if their values are left blank.

   Once the new option format is defined, its value is set in the same way as
   for a standard option. For example the following commands set a global
   value that applies to all subnets.

 "Dhcp4": {
     "option-data": [
         {
             "name": "foo",
             "code": 222,
             "space": "dhcp4",
             "csv-format": true,
             "data": "12345"
         }, ...
     ],
     ...
 }

   New options can take more complex forms than simple use of primitives
   (uint8, string, ipv4-address etc): it is possible to define an option
   comprising a number of existing primitives. Assume we want to define a new
   option that will consist of an IPv4 address, followed by an unsigned 16
   bit integer, followed by a boolean value, followed by a text string. Such
   an option could be defined in the following way:

 "Dhcp4": {
     "option-def": [
         {
             "name": "bar",
             "code": 223,
             "space": "dhcp4",
             "type": "record",
             "array": false,
             "record-types": "ipv4-address, uint16, boolean, string",
             "encapsulate": ""
         }, ...
     ],
     ...
 }

   The type is set to "record" to indicate that the option contains multiple
   values of different types. These types are given as a comma-separated list
   in the record-types field and should be those listed in Table 7.3, "List
   of standard DHCP option types".

   The values of the option are set as follows:

 "Dhcp4": {
     "option-data": [
         {
             "name": "bar",
             "space": "dhcp4",
             "code": 223,
             "csv-format": true,
             "data": "192.0.2.100, 123, true, Hello World"
         }
     ],
     ...
 }

   csv-format is set to true to indicate that the data field comprises a
   command-separated list of values. The values in the data must correspond
   to the types set in the record-types field of the option definition.

  Note

   In the general case, boolean values are specified as true or false,
   without quotes. Some specific boolean parameters may accept also "true",
   "false", 0, 1, "0" and "1". Future Kea versions will accept all those
   values for all boolean parameters.

  7.2.8. DHCPv4 Vendor Specific Options

   Currently there are three option spaces defined: "dhcp4" (used by the
   DHCPv4 daemon) and "dhcp6" (for the DHCPv6 daemon); there is also
   "vendor-encapsulated-options-space", which is empty by default, but
   options can be defined in it. Those options are called vendor-specific
   information options. The following examples show how to define an option
   "foo" with code 1 that consists of an IPv4 address, an unsigned 16 bit
   integer and a string. The "foo" option is conveyed in a vendor specific
   information option.

   The first step is to define the format of the option:

 "Dhcp4": {
     "option-def": [
         {
             "name": "foo",
             "code": 1,
             "space": "vendor-encapsulated-options-space",
             "type": "record",
             "array": false,
             "record-types": "ipv4-address, uint16, string",
             "encapsulates": ""
         }
     ],
     ...
 }

   (Note that the option space is set to
   "vendor-encapsulated-options-space".) Once the option format is defined,
   the next step is to define actual values for that option:

 "Dhcp4": {
     "option-data": [
         {
             "name": "foo",
             "space": "vendor-encapsulated-options-space",
             "code": 1,
             "csv-format": true,
             "data": "192.0.2.3, 123, Hello World"
         }
     ],
     ...
 }

   We also set up a dummy value for "vendor-encapsulated-options", the option
   that conveys our sub-option "foo". This is required else the option will
   not be included in messages sent to the client.

 "Dhcp4": {
     "option-data": [
         {
             "name": "vendor-encapsulated-options",
             "space": "dhcp4",
             "code": 43,
             "csv-format": false,
             "data": ""
         }
     ],
     ...
 }

  Note

   With this version of Kea, the "vendor-encapsulated-options" option must be
   specified in the configuration although it has no configurable parameters.
   If it is not specified, the server will assume that it is not configured
   and will not send it to a client. In the future there will be no need to
   include this option in the configuration.

  7.2.9. Nested DHCPv4 Options (Custom Option Spaces)

   It is sometimes useful to define completely new option space. This is the
   case when user creates new option in the standard option space ("dhcp4 or
   "dhcp6") and wants this option to convey sub-options. Since they are in a
   separate space, sub-option codes will have a separate numbering scheme and
   may overlap with the codes of standard options.

   Note that creation of a new option space when defining sub-options for a
   standard option is not required, because it is created by default if the
   standard option is meant to convey any sub-options (see Section 7.2.8,
   "DHCPv4 Vendor Specific Options").

   Assume that we want to have a DHCPv4 option called "container" with code
   222 that conveys two sub-options with codes 1 and 2. First we need to
   define the new sub-options:

 "Dhcp4": {
     "option-def": [
         {
             "name": "subopt1",
             "code": 1,
             "space": "isc",
             "type": "ipv4-address",
             "record-types": "",
             "array": false,
             "encapsulate ""
         },
         {
             "name": "subopt2",
             "code": 2,
             "space": "isc",
             "type": "string",
             "record-types": "",
             "array": false,
             "encapsulate": ""
         }
     ],
     ...
 }

   Note that we have defined the options to belong to a new option space (in
   this case, "isc").

   The next step is to define a regular DHCPv4 option with our desired code
   and specify that it should include options from the new option space:

 "Dhcp4": {
     "option-def": [
         ...,
         {
             "name": "container",
             "code": 222,
             "space": "dhcp4",
             "type": "empty",
             "array": false,
             "record-types": "",
             "encapsulate": "isc"
         }
     ],
     ...
 }

   The name of the option space in which the sub-options are defined is set
   in the "encapsulate" field. The "type" field is set to "empty" to indicate
   that this option does not carry any data other than sub-options.

   Finally, we can set values for the new options:

 "Dhcp4": {
     "option-data": [
         {
             "name": "subopt1",
             "space": "isc",
             "code": 1,
             "csv-format": true,
             "data": "192.0.2.3"
         },
         }
             "name": "subopt2",
             "space": "isc",
             "code": 2,
             "csv-format": true,
             "data": "Hello world"
         },
         {
             "name": "container",
             "space": "dhcp4",
             "code": 222,
             "csv-format": true,
             "data": ""
         }
     ],
     ...
 }

   Even though the "container" option does not carry any data except
   sub-options, the "data" field must be explicitly set to an empty value.
   This is required because in the current version of Kea, the default
   configuration values are not propagated to the configuration parsers: if
   the "data" is not set the parser will assume that this parameter is not
   specified and an error will be reported.

   Note that it is possible to create an option which carries some data in
   addition to the sub-options defined in the encapsulated option space. For
   example, if the "container" option from the previous example was required
   to carry an uint16 value as well as the sub-options, the "type" value
   would have to be set to "uint16" in the option definition. (Such an option
   would then have the following data structure: DHCP header, uint16 value,
   sub-options.) The value specified with the "data" parameter -- which
   should be a valid integer enclosed in quotes, e.g. "123" -- would then be
   assigned to the uint16 field in the "container" option.

  7.2.10. Unspecified parameters for DHCPv4 option configuration

   In many cases it is not required to specify all parameters for an option
   configuration and the default values may be used. However, it is important
   to understand the implications of not specifing some of them as it may
   result in configuration errors. The list below explains the behavior of
   the server when a particular parameter is not explicitly specified:

     o name - the server requires an option name or option code to identify
       an option. If this parameter is unspecified, the option code must be
       specified.
     o code - the server requires an option name or option code to identify
       an option. This parameter may be left unspecified if the name
       parameter is specified. However, this also requires that the
       particular option has its definition (it is either a standard option
       or an administrator created a definition for the option using an
       'option-def' structure), as the option definition associates an option
       with a particular name. It is possible to configure an option for
       which there is no definition (unspecified option format).
       Configuration of such options requires the use of option code.
     o space - if the option space is unspecified it will default to 'dhcp4'
       which is an option space holding DHCPv4 standard options.
     o data - if the option data is unspecified it defaults to an empty
       value. The empty value is mostly used for the options which have no
       payload (boolean options), but it is legal to specify empty values for
       some options which carry variable length data and which spec allows
       for the length of 0. For such options, the data parameter may be
       omitted in the configuration.
     o csv-format - if this value is not specified and the definition for the
       particular option exists, the server will assume that the option data
       is specified as a list of comma separated values to be assigned to
       individual fields of the DHCP option. If the definition does not exist
       for this option, the server will assume that the data parameter
       contains the option payload in the binary format (represented as a
       string of hexadecimal digits). Note that not specifying this parameter
       doesn't imply that it defaults to a fixed value, but the configuration
       data interpretation also depends on the presence of the option
       definition. An administrator must be aware if the definition for the
       particular option exists when this parameter is not specified. It is
       generally recommended to not specify this parameter only for the
       options for which the definition exists, e.g. standard options.
       Setting csv-format to an explicit value will cause the server to
       strictly check the format of the option data specified.

  7.2.11. Stateless Configuration of DHCPv4 clients

   The DHCPv4 server supports the stateless client configuration whereby the
   client has an IP address configured (e.g. using manual configuration) and
   only contacts the server to obtain other configuration parameters, e.g.
   DNS servers' addresses. In order to obtain the stateless configuration
   parameters the client sends the DHCPINFORM message to the server with the
   "ciaddr" set to the address that the client is currently using. The server
   unicasts the DHCPACK message to the client that includes the stateless
   configuration ("yiaddr" not set).

   The server will respond to the DHCPINFORM when the client is associated
   with the particular subnet defined in the server's configuration. The
   example subnet configuration will look like this:

 "Dhcp4": {
     "subnet4": [
         {
             "subnet": "192.0.2.0/24"
             "option-data": [ {
                 "name": "domain-name-servers",
                 "code": 6,
                 "data": "192.0.2.200,192.0.2.201",
                 "csv-format": true,
                 "space": "dhcp4"
             } ]
         }
     ]
 }

   This subnet specifies the single option which will be included in the
   DHCPACK message to the client in response to DHCPINFORM. Note that the
   subnet definition does not require the address pool configuration if it
   will be used solely for the stateless configuration.

   This server will associate the subnet with the client if one of the
   following conditions is met:

     o The DHCPINFORM is relayed and the giaddr matches the configured
       subnet.
     o The DHCPINFORM is unicast from the client and the ciaddr matches the
       configured subnet.
     o The DHCPINFORM is unicast from the client, the ciaddr is not set but
       the source address of the IP packet matches the configured subnet.
     o The DHCPINFORM is not relayed and the IP address on the interface on
       which the message is received matches the configured subnet.

  7.2.12. Client Classification in DHCPv4

  Note

   The DHCPv4 server has been extended to support limited client
   classification. Although the current capability is modest, it is expected
   to be expanded in the future. However, it is envisaged that the majority
   of client classification extensions will be using hooks extensions.

   In certain cases it is useful to differentiate between different types of
   clients and treat them differently. The process of doing classification is
   conducted in two steps. The first step is to assess an incoming packet and
   assign it to zero or more classes. This classification is currently
   simple, but is expected to grow in capability soon. Currently the server
   checks whether an incoming packet includes the vendor class identifier
   option (60). If it does, the content of that option is prepended with
   "VENDOR_CLASS_" then it is interpreted as a class. For example, modern
   cable modems will send this option with value "docsis3.0" and as a result
   the packet will belong to class "VENDOR_CLASS_docsis3.0".

   It is envisaged that the client classification will be used for changing
   the behavior of almost any part of the DHCP message processing, including
   assigning leases from different pools, assigning different options (or
   different values of the same options) etc. For now, there are only two
   mechanisms that are taking advantage of client classification: specific
   processing for cable modems and subnet selection.

   For clients that belong to the VENDOR_CLASS_docsis3.0 class, the siaddr
   field is set to the value of next-server (if specified in a subnet). If
   there is a boot-file-name option specified, its value is also set in the
   file field in the DHCPv4 packet. For eRouter1.0 class, the siaddr is
   always set to 0.0.0.0. That capability is expected to be moved to an
   external hook library that will be dedicated to cable modems.

   Kea can be instructed to limit access to given subnets based on class
   information. This is particularly useful for cases where two types of
   devices share the same link and are expected to be served from two
   different subnets. The primary use case for such a scenario is cable
   networks. There are two classes of devices: the cable modem itself, which
   should be handed a lease from subnet A and all other devices behind the
   modem that should get a lease from subnet B. That segregation is essential
   to prevent overly curious users from playing with their cable modems. For
   details on how to set up class restrictions on subnets, see
   Section 7.2.12.1, "Limiting Access to IPv4 Subnet to Certain Classes".

    7.2.12.1. Limiting Access to IPv4 Subnet to Certain Classes

   In certain cases it beneficial to restrict access to certain subnets only
   to clients that belong to a given subnet. For details on client classes,
   see Section 7.2.12, "Client Classification in DHCPv4". This is an
   extension of a previous example from Section 7.2.5, "Configuration of IPv4
   Address Pools". Let's assume that the server is connected to a network
   segment that uses the 192.0.2.0/24 prefix. The Administrator of that
   network has decided that addresses from range 192.0.2.10 to 192.0.2.20 are
   going to be managed by the Dhcp4 server. Only clients belonging to client
   class VENDOR_CLASS_docsis3.0 are allowed to use this subnet. Such a
   configuration can be achieved in the following way:

 "Dhcp4": {
     "subnet4": [
         {
             "subnet": "192.0.2.0/24",
             "pools": [ { "pool": "192.0.2.10 - 192.0.2.20" } ],
             "client-class": "VENDOR_CLASS_docsis3.0"
         }
     ],
     ...
 }

   Care should be taken with client classification as it is easy for clients
   that do not meet class criteria to be denied any service altogether.

  7.2.13. Configuring DHCPv4 for DDNS

   As mentioned earlier, kea-dhcp4 can be configured to generate requests to
   the DHCP-DDNS server (referred to here as "D2" ) to update DNS entries.
   These requests are known as NameChangeRequests or NCRs. Each NCR contains
   the following information:

    1. Whether it is a request to add (update) or remove DNS entries

    2. Whether the change requests forward DNS updates (A records), reverse
       DNS updates (PTR records), or both.

    3. The FQDN, lease address, and DHCID

   The parameters for controlling the generation of NCRs for submission to D2
   are contained in the dhcp-ddns section of the kea-dhcp4 server
   configuration. The mandatory parameters for the DHCP DDNS configuration
   are enable-updates which is unconditionally required, and
   qualifying-suffix which has no default value and is required when
   enable-updates is set to true. The two (disabled and enabled) minimal DHCP
   DDNS configurations are:

 "Dhcp4": {
     "dhcp-ddns": {
         "enable-updates": false
     },
     ...
 }

   and for example:

 "Dhcp4": {
     "dhcp-ddns": {
         "enable-updates": true,
         "qualifying-suffix": "example."
     },
     ...
 }

   The default values for the "dhcp-ddns" section are as follows:

     o "server-ip": "127.0.0.1"
     o "server-port": 53001
     o "sender-ip": ""
     o "sender-port": 0
     o "max-queue-size": 1024
     o "ncr-protocol": "UDP"
     o "ncr-format": "JSON"
     o "override-no-update": false
     o "override-client-update": false
     o "replace-client-name": false
     o "generated-prefix": "myhost"

    7.2.13.1. DHCP-DDNS Server Connectivity

   In order for NCRs to reach the D2 server, kea-dhcp4 must be able to
   communicate with it. kea-dhcp4 uses the following configuration parameters
   to control how it communications with D2:

     o enable-updates - determines whether or not kea-dhcp4 will generate
       NCRs. By default, this value is false hence DDNS updates are disabled.
       To enable DDNS updates set this value to true:
     o server-ip - IP address on which D2 listens for requests. The default
       is the local loopback interface at address 127.0.0.1. You may specify
       either an IPv4 or IPv6 address.
     o server-port - port on which D2 listens for requests. The default value
       is 53001.
     o sender-ip - IP address which kea-dhcp4 should use to send requests to
       D2. The default value is blank which instructs kea-dhcp4 to select a
       suitable address.
     o sender-port - port which kea-dhcp4 should use to send requests to D2.
       The default value of 0 instructs kea-dhcp4 to select a suitable port.
     o max-queue-size - maximum number of requests allowed to queue waiting
       to be sent to D2. This value guards against requests accumulating
       uncontrollably if they are being generated faster than they can be
       delivered. If the number of requests queued for transmission reaches
       this value, DDNS updating will be turned off until the queue backlog
       has been sufficiently reduced. The intention is to allow the kea-dhcp4
       server to continue lease operations without running the risk that its
       memory usage grows without limit. The default value is 1024.
     o ncr-format - socket protocol use when sending requests to D2.
       Currently only UDP is supported. TCP may be available in an upcoming
       release.
     o ncr-protocol - packet format to use when sending requests to D2.
       Currently only JSON format is supported. Other formats may be
       available in future releases.

   By default, kea-dhcp-ddns is assumed to be running on the same machine as
   kea-dhcp4, and all of the default values mentioned above should be
   sufficient. If, however, D2 has been configured to listen on a different
   address or port, these values must be altered accordingly. For example, if
   D2 has been configured to listen on 192.168.1.10 port 900, the following
   configuration would be required:

 "Dhcp4": {
     "dhcp-ddns": {
         "server-ip": "192.168.1.10",
         "server-port": 900,
         ...
     },
     ...
 }

    7.2.13.2. When Does the kea-dhcp4 Server Generate DDNS Requests?

   kea-dhcp4 follows the behavior prescribed for DHCP servers in RFC 4702. It
   is important to keep in mind that kea-dhcp4 provides the initial decision
   making of when and what to update and forwards that information to D2 in
   the form of NCRs. Carrying out the actual DNS updates and dealing with
   such things as conflict resolution are within the purview of D2 itself
   (Chapter 9, The DHCP-DDNS Server). This section describes when kea-dhcp4
   will generate NCRs and the configuration parameters that can be used to
   influence this decision. It assumes that the "enable-updates" parameter is
   true.

   In general, kea-dhcp4 will generate DDNS update requests when:

    1. A new lease is granted in response to a DHCP REQUEST

    2. An existing lease is renewed but the FQDN associated with it has
       changed.

    3. An existing lease is released in response to a DHCP RELEASE

   In the second case, lease renewal, two DDNS requests will be issued: one
   request to remove entries for the previous FQDN and a second request to
   add entries for the new FQDN. In the last case, a lease release, a single
   DDNS request to remove its entries will be made. The decision making
   involved when granting a new lease (the first case) is more involved and
   is discussed next.

   When a new lease is granted, kea-dhcp4 will generate a DDNS update request
   if the DHCP REQUEST contains either the FQDN option (code 81) or the Host
   Name option (code 12). If both are present, the server will use the FQDN
   option. By default kea-dhcp4 will respect the FQDN N and S flags specified
   by the client as shown in the following table:

   Table 7.4. Default FQDN Flag Behavior

   +------------------------------------------------------------------------+
   | Client    | Client Intent           | Server Response    | Server      |
   | Flags:N-S |                         |                    | Flags:N-S-O |
   |-----------+-------------------------+--------------------+-------------|
   |           | Client wants to do      | Server generates   |             |
   | 0-0       | forward updates, server | reverse-only       | 1-0-0       |
   |           | should do reverse       | request            |             |
   |           | updates                 |                    |             |
   |-----------+-------------------------+--------------------+-------------|
   |           | Server should do both   | Server generates   |             |
   | 0-1       | forward and reverse     | request to update  | 0-1-0       |
   |           | updates                 | both directions    |             |
   |-----------+-------------------------+--------------------+-------------|
   | 1-0       | Client wants no updates | Server does not    | 1-0-0       |
   |           | done                    | generate a request |             |
   +------------------------------------------------------------------------+

   The first row in the table above represents "client delegation". Here the
   DHCP client states that it intends to do the forward DNS updates and the
   server should do the reverse updates. By default, kea-dhcp4 will honor the
   client's wishes and generate a DDNS request to the DHCP-DDNS server to
   update only reverse DNS data. The parameter override-client-update can be
   used to instruct the server to override client delegation requests. When
   this parameter is true, kea-dhcp4 will disregard requests for client
   delegation and generate a DDNS request to update both forward and reverse
   DNS data. In this case, the N-S-O flags in the server's response to the
   client will be 0-1-1 respectively.

   (Note that the flag combination N=1, S=1 is prohibited according to RFC
   4702. If such a combination is received from the client, the packet will
   be dropped by kea-dhcp4.)

   To override client delegation, set the following values in your
   configuration file:

 "Dhcp4": {
     "dhcp-ddns": {
         "override-client-update": true,
         ...
     },
     ...
 }

   The third row in the table above describes the case in which the client
   requests that no DNS updates be done. The parameter, override-no-update,
   can be used to instruct the server to disregard the client's wishes. When
   this parameter is true, kea-dhcp4 will generate a DDNS update request to
   kea-dhcp-ddns even if the client requests that no updates be done. The
   N-S-O flags in the server's response to the client will be 0-1-1.

   To override client delegation, the following values should be set in your
   configuration:

 "Dhcp4": {
     "dhcp-ddns": {
         "override-no-update": true,
         ...
     },
     ...
 }

   kea-dhcp4 will always generate DDNS update requests if the client request
   only contains the Host Name option. In addition it will include an FQDN
   option in the response to the client with the FQDN N-S-O flags set to
   0-1-0 respectively. The domain name portion of the FQDN option will be the
   name submitted to D2 in the DDNS update request.

    7.2.13.3. kea-dhcp4 name generation for DDNS update requests

   Each NameChangeRequest must of course include the fully qualified domain
   name whose DNS entries are to be affected. kea-dhcp4 can be configured to
   supply a portion or all of that name based upon what it receives from the
   client in the DHCP REQUEST.

   The rules for determining the FQDN option are as follows:

    1. If configured to do, so ignore the REQUEST contents and generate a
       FQDN using a configurable prefix and suffix.

    2. If the REQUEST contains the client FQDN option, the candidate name is
       taken from there, otherwise it is taken from the Host Name option. The
       candidate name may then be modified:

         a. If the candidate name is a fully qualified domain name, use it.

         b. If the candidate name is a partial (i.e. unqualified) name then
            add a configurable suffix to the name and use the result as the
            FQDN.

         c. If the candidate name is a empty, generate a FQDN using a
            configurable prefix and suffix.

   To instruct kea-dhcp4 to always generate the FQDN for a client, set the
   parameter replace-client-name to true as follows:

 "Dhcp4": {
     "dhcp-ddns": {
         "replace-client-name": true,
         ...
     },
     ...
 }

   The prefix used in the generation of a FQDN is specified by the
   generated-prefix parameter. The default value is "myhost". To alter its
   value simply set it to the desired string:

 "Dhcp4": {
     "dhcp-ddns": {
         "generated-prefix": "another.host",
         ...
     },
     ...
 }

   The suffix used when generating a FQDN or when qualifying a partial name
   is specified by the qualifying-suffix parameter. This parameter has no
   default value, thus it is mandatory when DDNS updates are enabled. To set
   its value simply set it to the desired string:

 "Dhcp4": {
     "dhcp-ddns": {
         "qualifying-suffix": "foo.example.org",
         ...
     },
     ...
 }

   When generating a name, kea-dhcp4 will construct name of the format:

   [generated-prefix]-[address-text].[qualifying-suffix].

   where address-text is simply the lease IP address converted to a
   hyphenated string. For example, if the lease address is 172.16.1.10, the
   qualifying suffix "example.com", and the default value is used for
   generated-prefix, the generated FQDN would be:

   myhost-172-16-1-10.example.com.

  7.2.14. Next Server (siaddr)

   In some cases, clients want to obtain configuration from the TFTP server.
   Although there is a dedicated option for it, some devices may use the
   siaddr field in the DHCPv4 packet for that purpose. That specific field
   can be configured using next-server directive. It is possible to define it
   in the global scope or for a given subnet only. If both are defined, the
   subnet value takes precedence. The value in subnet can be set to 0.0.0.0,
   which means that next-server should not be sent. It may also be set to an
   empty string, which means the same as if it was not defined at all, i.e.
   use the global value.

 "Dhcp4": {
     "next-server": "192.0.2.123",
     ...,
     "subnet4": [
         {
             "next-server": "192.0.2.234",
             ...
         }
     ]
 }

  7.2.15. Echoing Client-ID (RFC 6842)

   The original DHCPv4 specification (RFC 2131) states that the DHCPv4 server
   must not send back client-id options when responding to clients. However,
   in some cases that confused clients that did not have MAC address or
   client-id; see RFC 6842. for details. That behavior has changed with the
   publication of RFC 6842. which updated RFC 2131. That update now states
   that the server must send client-id if the client sent it. That is the
   default behaviour that Kea offers. However, in some cases older devices
   that do not support RFC 6842. may refuse to accept responses that include
   the client-id option. To enable backward compatibility, an optional
   configuration parameter has been introduced. To configure it, use the
   following configuration statement:

 "Dhcp4": {
     "echo-client-id": false,
     ...
 }

7.3. Host reservation in DHCPv4

   There are many cases where it is useful to provide a configuration on a
   per host basis. The most obvious one is to reserve specific, static
   address for exclusive use by a given client (host) - returning client will
   receive the same address from the server every time, and other clients
   will generally not receive that address. Note that there may be cases when
   the new reservation has been made for the client for the address being
   currently in use by another client. We call this situation a "conflict".
   The conflicts get resolved automatically over time as described in the
   subsequent sections. Once conflict is resolved,the client will keep
   receiving the reserved configuration when it renews.

   Another example when the host reservations are applicable is when a host
   that has specific requirements, e.g. a printer that needs additional DHCP
   options. Yet another possible use case is to define unique names for
   hosts. Although not all of the presented use cases are implemented yet,
   Kea software will support them in the near future.

   Hosts reservations are defined as parameters for each subnet. Each host
   has to be identified by its hardware/MAC address. There is an optional
   reservations array in the Subnet4 element. Each element in that array is a
   structure, that holds information about reservrations for a single host.
   In particular, such a structure has to have an indentifer that uniquely
   identifies a host. In DHCPv4 context, such an identifier is a hardware or
   MAC address. In most cases, also an address will be specified. It is
   possible to specify a hostname. Additional capabilities are planned.

   The following example shows how to reserve addresses for specific hosts:

 "subnet4": [
     {
         "pools": [ { "pool":  "192.0.2.1 - 192.0.2.200" } ],
         "subnet": "192.0.2.0/24",
         "interface": "eth0",
         "reservations": [
             {
                 "hw-address": "1a:1b:1c:1d:1e:1f",
                 "ip-address": "192.0.2.202"
             },
             {
                 "hw-address": "0a:0b:0c:0d:0e:0f",
                 "ip-address": "192.0.2.100",
                 "hostname": "alice-laptop"
             }
         ]
     }
 ]

   The first entry reserves the 192.0.2.202 address for the client that uses
   MAC adress of 1a:1b:1c:1d:1e:1f. The second entry reserves the address
   192.0.2.100 and the hostname of alice-laptop for client using MAC address
   0a:0b:0c:0d:0e:0f. Note that if you plan to do DNS updates, it is strongly
   recommended for the hostnames to be unique.

   Making a reservation for a mobile host that may visit multiple subnets
   requires a separate host definition in each subnet it is expected to
   visit. It is not allowed to define multiple host definitions with the same
   hardware address in a single subnet. It is a valid configuration, if such
   definitions are specified in different subnets, though.

   Adding host reservation incurs a performance penalty. In principle, when
   the server that does not support host reservation responds to a query, it
   needs to check whether there is a lease for a given address being
   considered for allocation or renewal. The server that also supports host
   reservation, has to perform additional checks: not only if the address is
   currently used (if there is a lease for it), but also whether the address
   could be used by someone else (if there is a reservation for it). That
   additional check incurs performance penalty.

  7.3.1. Address reservation types

   In a typical scenario there is an IPv4 subnet defined, e.g. 192.0.2.0/24,
   with certain part of it dedicated for dynamic allocation by the DHCPv4
   server. That dynamic part is referred to as a dynamic pool or simply a
   pool. In principle, the host reservation can reserve any address that
   belongs to the subnet. The reservations that specify addresses that belong
   to configured pools are called in-pool reservations. In contrast, those
   that do not belong to dynamic pools are called out-of-pool reservations.
   There is no formal difference in the reservation syntax. As of 0.9.1, both
   reservation types are handled uniformly. However, upcoming releases may
   offer improved performance if there are only out-of-pool reservations as
   the server will be able to skip reservation checks when dealing with
   existing leases. Therefore, system administrators are encouraged to use
   out-of-pool reservations, if possible.

  7.3.2. Conflicts in DHCPv4 reservations

   As the reservations and lease information are stored separately, conflicts
   may arise. Consider the following series of events. The server has
   configured the dynamic pool of addresses from the range of 192.0.2.10 to
   192.0.2.20. The Host A requests an address and gets 19.0.2.10. Now the
   system administrator decides to reserve the address for the Host B. He
   decides to reserve 192.0.2.10 for that purpose. In general, reserving an
   address that is currently assigned to someone else is not recommended, but
   there are valid use cases where such an operation is warranted.

   The server now has a conflict to resolve. Let's analyze the situation
   here. If the Host B boots up and requests an address, the server is not
   able to assign the reserved address 192.0.2.10 for the Host B. A naive
   approach would to be immediately remove the existing lease for the Host A
   and create a new one for the Host B. That would not solve the problem,
   though, because as soon as the Host B gets the address, it will detect
   that the address is already in use by the Host A and would send the
   DHCPDECLINE message. Therefore, in this situation, the server has to
   temporarily assign a different address (not matching what has been
   reserved) to the Host B.

   When the Host A renews its address, the server will discover that the
   address being renewed is now reserved for another host - the Host B.
   Therefore the server will inform the Host A that it is no longer allowed
   to use it by sending DHCPNAK message. The server will not remove the
   lease, though, as there's small chance that the DHCPNAK may be lost if the
   network is lossy. If that happens, the client will not receive any
   responses, so it will retransmit its DHCPREQUEST packet. Once the DHCPNAK
   is received by the Host A, it will then revert to the server discovery and
   will eventually get a different address. Besides allocating a new lease,
   the server will also remove the old one. As a result, the address
   192.0.2.10 will be no longer used. When Host B tries to renew its
   temporarily assigned address, the server will detect that it has a valid
   lease, but there is a reservation for a different address. The server will
   send DHCPNAK to inform Host B that its address is no longer usable, but
   will keep its lease (again, the DHCPNAK may be lost, so the server will
   keep it, until the client returns for a new address). The Host B will
   revert to the server discovery phase and will eventually send a
   DHCPREQUEST message. This time the server will find out that there is a
   reservation for that host and the reserved address 192.0.2.10 is not used,
   so it will be granted. It will also remove the lease for the temporarily
   assigned address that the Host B previously obtained.

   This recovery will succeed, even if other hosts will attempt to get the
   reserved address. Had the Host C requested address 192.0.2.10 after the
   reservation was made, the server will either offer a different address
   (when responding to DHCPDISCOVER) or would send DHCPNAK (when responding
   to DHCPREQUEST).

   This recovery mechanism allows the server to fully recover from a case
   where reservations conflict with the existing leases. This procedure takes
   time and will roughly take as long as renew-timer value specified. The
   best way to avoid such recovery is to not define new reservations that
   conflict with existing leases. Another recommendation is to use
   out-of-pool reservations. If the reserved address does not belong to a
   pool, there is no way that other clients could get this address (note that
   having multiple reservations for the same address is not allowed).

  7.3.3. Reserving a hostname

   When the reservation for the client includes the hostname , the server
   will assign this hostname to the client and send it back in the Client
   FQDN or Hostname option, depending on which of them the client has sent to
   the server. The reserved hostname always takes precedence over the
   hostname supplied by the client or the autogenerated (from the IPv4
   address) hostname.

   The server qualifies the reserved hostname with the value of the
   qualifying-suffix parameter. For example, the following subnet
   configuration:

     {
         "subnet4": [ {
             "subnet": "10.0.0.0/24",
             "pools": [ { "pool": "10.0.0.10-10.0.0.100" } ],
             "reservations": [
                {
                  "hw-address": "aa:bb:cc:dd:ee:ff",
                  "hostname": "alice-laptop"
                }
             ]
          }],
         "dhcp-ddns": {
             "enable-updates": true,
             "qualifying-suffix": "example.isc.org."
         }
     }

   will result in assigning the "alice-laptop.example.isc.org." hostname to
   the client using the MAC address "aa:bb:cc:dd:ee:ff". If the
   qualifying-suffix is not specified, the default (empty) value will be
   used, and in this case the value specified as a hostname will be treated
   as fully qualified name. Thus, by leaving the qualifying-suffix empty it
   is possible to qualify hostnames for the different clients with different
   domain names:

     {
         "subnet4": [ {
             "subnet": "10.0.0.0/24",
             "pools": [ { "pool": "10.0.0.10-10.0.0.100" } ],
             "reservations": [
                {
                  "hw-address": "aa:bb:cc:dd:ee:ff",
                  "hostname": "alice-laptop.isc.org."
                },
                {
                  "hw-address": "12:34:56:78:99:AA",
                  "hostname": "mark-desktop.example.org."
                }

             ]
          }],
         "dhcp-ddns": {
             "enable-updates": true,
         }
     }

  7.3.4. Reserving specific options

   Currently it is not possible to specify options in host reservation. Such
   a feature will be added in the upcoming Kea releases.

  7.3.5. Fine Tuning IPv4 Host Reservation

  Note

   reservation-mode configuration parameter in DHCPv4 server is accepted, but
   not used in the Kea 0.9.1 beta. Full implementation will be available in
   the upcoming releases.

   Host reservation capability introduces additional restrictions for the
   allocation engine during lease selection and renewal. In particular, three
   major checks are necessary. First, when selecting a new lease, it is not
   sufficient for a candidate lease to be not used by another DHCP client. It
   also must not be reserved for another client. Second, when renewing a
   lease, additional check must be performed whether the address being
   renewed is not reserved for another client. Finally, when a host renews an
   address, the server has to check whether there's a reservation for this
   host, so the exisiting (dynamically allocated) address should be revoked
   and the reserved one be used instead.

   Some of those checks may be unnecessary in certain deployments. Not
   performing them may improve performance. The Kea server provides the
   reservation-mode configuration parameter to select the types of
   reservations allowed for the particular subnet. Each reservation type has
   different constraints for the checks to be performed by the server when
   allocating or renewing a lease for the client. Allowed values are:

     o all - enables all host reservation types. This is the default value.
       This setting is the safest and the most flexible. It allows in-pool
       and out-of-pool reservations. As all checks are conducted, it is also
       the slowest.
     o out-of-pool - allows only out of pool host reservations. With this
       setting in place, the server may assume that all host reservations are
       for addresses that do not belong to the dynamic pool. Therefore it can
       skip the reservation checks when dealing with in-pool addresses, thus
       improving performance. Do not use this mode if any of your
       reservations use in-pool address. Caution is advised when using this
       setting. Kea 0.9.1 does not sanity check the reservations against
       reservation-mode. Misconfiguration may cause problems.
     o disabled - host reservation support is disabled. As there are no
       reservations, the server will skip all checks. Any reservations
       defined will be completely ignored. As the checks are skipped, the
       server may operate faster in this mode.

   An example configuration that disables reservation looks like follows:

 "Dhcp4": {
     "subnet4": [
         {
         "subnet": "192.0.2.0/24",
         "reservation-mode": "disabled",
         ...
         }
     ]
 }

7.4. Server Identifier in DHCPv4

   The DHCPv4 protocol uses a "server identifier" to allow clients to
   discriminate between several servers present on the same link: this value
   is an IPv4 address of the server. The server chooses the IPv4 address of
   the interface on which the message from the client (or relay) has been
   received. A single server instance will use multiple server identifiers if
   it is receiving queries on multiple interfaces.

   Currently there is no mechanism to override the default server identifiers
   by an administrator. In the future, the configuration mechanism will be
   used to specify the custom server identifier.

7.5. How the DHCPv4 Server Selects a Subnet for the Client

   The DHCPv4 server differentiates between the directly connected clients,
   clients trying to renew leases and clients sending their messages through
   relays. For the directly connected clients the server will check the
   configuration for the interface on which the message has been received,
   and if the server configuration doesn't match any configured subnet the
   message is discarded.

   Assuming that the server's interface is configured with the IPv4 address
   192.0.2.3, the server will only process messages received through this
   interface from a directly connected client if there is a subnet configured
   to which this IPv4 address belongs, e.g. 192.0.2.0/24. The server will use
   this subnet to assign IPv4 address for the client.

   The rule above does not apply when the client unicasts its message, i.e.
   is trying to renew its lease. Such a message is accepted through any
   interface. The renewing client sets ciaddr to the currently used IPv4
   address. The server uses this address to select the subnet for the client
   (in particular, to extend the lease using this address).

   If the message is relayed it is accepted through any interface. The giaddr
   set by the relay agent is used to select the subnet for the client.

   It is also possible to specify a relay IPv4 address for a given subnet. It
   can be used to match incoming packets into a subnet in uncommon
   configurations, e.g. shared subnets. See Section 7.5.1, "Using a Specific
   Relay Agent for a Subnet" for details.

  Note

   The subnet selection mechanism described in this section is based on the
   assumption that client classification is not used. The classification
   mechanism alters the way in which a subnet is selected for the client,
   depending on the classes to which the client belongs.

  7.5.1. Using a Specific Relay Agent for a Subnet

   The relay has to have an interface connected to the link on which the
   clients are being configured. Typically the relay has an IPv4 address
   configured on that interface that belongs to the subnet from which the
   server will assign addresses. In the typical case, the server is able to
   use the IPv4 address inserted by the relay (in the giaddr field of the
   DHCPv4 packet) to select the appropriate subnet.

   However, that is not always the case. In certain uncommon -- valid --
   deployments, the relay address may not match the subnet. This usually
   means that there is more than one subnet allocated for a given link. The
   two most common examples where this is the case are long lasting network
   renumbering (where both old and new address space is still being used) and
   a cable network. In a cable network both cable modems and the devices
   behind them are physically connected to the same link, yet they use
   distinct addressing. In such a case, the DHCPv4 server needs additional
   information (the IPv4 address of the relay) to properly select an
   appropriate subnet.

   The following example assumes that there is a subnet 192.0.2.0/24 that is
   accessible via a relay that uses 10.0.0.1 as its IPv4 address. The server
   will be able to select this subnet for any incoming packets that came from
   a relay that has an address in 192.0.2.0/24 subnet. It will also select
   that subnet for a relay with address 10.0.0.1.

 "Dhcp4": {
     "subnet4": [
         {
             "subnet": "192.0.2.0/24",
             "pools": [ { "pool": "192.0.2.10 - 192.0.2.20" } ],
             "relay": {
                 "ip-address": "10.0.0.1"
             },
             ...
         }
     ],
     ...
 }

  7.5.2. Segregating IPv4 Clients in a Cable Network

   In certain cases, it is useful to mix relay address information,
   introduced in Section 7.5.1, "Using a Specific Relay Agent for a Subnet"
   with client classification, explained in Section 7.2.12.1, "Limiting
   Access to IPv4 Subnet to Certain Classes". One specific example is cable
   network, where typically modems get addresses from a different subnet than
   all devices connected behind them.

   Let's assume that there is one CMTS (Cable Modem Termination System) with
   one CM MAC (a physical link that modems are connected to). We want the
   modems to get addresses from the 10.1.1.0/24 subnet, while everything
   connected behind modems should get addresses from another subnet
   (192.0.2.0/24). The CMTS that acts as a relay uses address 10.1.1.1. The
   following configuration can serve that configuration:

 "Dhcp4": {
     "subnet4": [
         {
             "subnet": "10.1.1.0/24",
             "pools":  [ { "pool": "10.1.1.2 - 10.1.1.20" } ],
             "client-class" "docsis3.0",
             "relay": {
                 "ip-address": "10.1.1.1"
             }
         },
         {
             "subnet": "192.0.2.0/24",
             "pools": [ { "pool": "192.0.2.10 - 192.0.2.20" } ],
             "relay": {
                 "ip-address": "10.1.1.1"
             }
         }
     ],
     ...
 }

7.6. Supported DHCP Standards

   The following standards are currently supported:

     o Dynamic Host Configuration Protocol, RFC 2131: Supported messages are
       DISCOVER (1), OFFER (2), REQUEST (3), RELEASE (7), INFORM (8), ACK
       (5), and NAK(6).
     o DHCP Options and BOOTP Vendor Extensions, RFC 2132: Supported options
       are: PAD (0), END(255), Message Type(53), DHCP Server Identifier (54),
       Domain Name (15), DNS Servers (6), IP Address Lease Time (51), Subnet
       mask (1), and Routers (3).
     o DHCP Relay Agent Information Option, RFC 3046: Relay Agent Information
       option is supported.
     o Vendor-Identifying Vendor Options for Dynamic Host Configuration
       Protocol version 4, RFC 3925: Vendor-Identifying Vendor Class and
       Vendor-Identifying Vendor-Specific Information options are supported.
     o Client Identifier Option in DHCP Server Replies, RFC 6842: Server by
       default sends back client-id option. That capability may be disabled.
       See Section 7.2.15, "Echoing Client-ID (RFC 6842)" for details.

7.7. DHCPv4 Server Limitations

   These are the current limitations of the DHCPv4 server software. Most of
   them are reflections of the current stage of development and should be
   treated as "not implemented yet", rather than actual limitations. However,
   some of them are implications of the design choices made. Those are
   clearly marked as such.

     o Removal of a subnet during server reconfiguration may cause
       renumbering of auto-generated subnet identifiers, as described in
       section Section 7.2.4, "IPv4 Subnet Identifier".
     o Host reservation (static addresses) is not supported yet.
     o Full featured client classification is not supported yet.
     o BOOTP (RFC 951) is not supported. This is a design choice. BOOTP
       support is not planned.
     o On Linux and BSD system families the DHCP messages are sent and
       received over the raw sockets (using LPF and BPF) and all packet
       headers (including data link layer, IP and UDP headers) are created
       and parsed by Kea, rather than the system kernel. Currently, Kea can
       only parse the data link layer headers with a format adhering to IEEE
       802.3 standard and assumes this data link layer header format for all
       interfaces. Hence, Kea will fail to work on interfaces which use
       different data link layer header formats (e.g. Infiniband).
     o The DHCPv4 server does not verify that assigned address is unused.
       According to RFC 2131, the allocating server should verify that
       address is not used by sending ICMP echo request.
     o Address duplication report (DECLINE) is not supported yet.
     o The server doesn't act upon expired leases. In particular, when a
       lease expires, the server doesn't request the removal of the DNS
       records associated with it. Expired leases can be recycled.

Chapter 8. The DHCPv6 Server

   Table of Contents

   8.1. Starting and Stopping the DHCPv6 Server

   8.2. DHCPv6 Server Configuration

                8.2.1. Introduction

                8.2.2. Lease Storage

                8.2.3. Interface selection

                8.2.4. IPv6 Subnet Identifier

                8.2.5. Unicast traffic support

                8.2.6. Subnet and Address Pool

                8.2.7. Subnet and Prefix Delegation Pools

                8.2.8. Standard DHCPv6 options

                8.2.9. Custom DHCPv6 options

                8.2.10. DHCPv6 vendor specific options

                8.2.11. Nested DHCPv6 options (custom option spaces)

                8.2.12. Unspecified parameters for DHCPv6 option
                configuration

                8.2.13. IPv6 Subnet Selection

                8.2.14. DHCPv6 Relays

                8.2.15. Relay-Supplied Options

                8.2.16. Client Classification in DHCPv6

                8.2.17. Limiting access to IPv6 subnet to certain classes

                8.2.18. Configuring DHCPv6 for DDNS

   8.3. Host reservation in DHCPv6

                8.3.1. Address/prefix reservation types

                8.3.2. Conflicts in DHCPv6 reservations

                8.3.3. Reserving a hostname

                8.3.4. Reserving specific options

                8.3.5. Fine Tuning IPv6 Host Reservation

   8.4. Server Identifier in DHCPv6

   8.5. Stateless DHCPv6 (Information-Request Message)

   8.6. Using specific relay agent for a subnet

   8.7. Segregating IPv6 clients in a cable network

   8.8. MAC/Hardware addresses in DHCPv6

   8.9. Supported DHCPv6 Standards

   8.10. DHCPv6 Server Limitations

8.1. Starting and Stopping the DHCPv6 Server

   It is recommended that the Kea DHCPv6 server be started and stopped using
   keactrl (described in Chapter 6, Managing Kea with keactrl). However, it
   is also possible to run the server directly: it accepts the following
   command-line switches:

     o -c file - specifies the configuration file. This is the only mandatory
       switch.
     o -d - specifies whether the server logging should be switched to
       verbose mode. In verbose mode, the logging severity and debuglevel
       specified in the configuration file are ignored and "debug" severity
       and the maximum debuglevel (99) are assumed. The flag is convenient,
       for temporarily switching the server into maximum verbosity, e.g. when
       debugging.
     o -p port - specifies UDP port on which the server will listen. This is
       only useful during testing, as a DHCPv6 server listening on ports
       other than default DHCPv6 ports will not be able to handle regular
       DHCPv6 queries.
     o -v - prints out Kea version and exits.
     o -V - prints out Kea extended version with additional parameters and
       exits.

   When running in a console, the server can be shut down by pressing ctrl-c.
   It detects the key combination and shuts down gracefully.

   On start-up, the server will detect available network interfaces and will
   attempt to open UDP sockets on all interfaces mentioned in the
   configuration file.

   Since the DHCPv6 server opens privileged ports, it requires root access.
   Make sure you run this daemon as root.

8.2. DHCPv6 Server Configuration

  8.2.1. Introduction

   This section explains how to configure the DHCPv6 server using the Kea
   configuration backend. (Kea configuration using any other backends is
   outside of scope of this document.) Before DHCPv6 is started, its
   configuration file has to be created. The basic configuration looks as
   follows:

 {
 # DHCPv6 configuration starts on the next line
 "Dhcp6": {

 # First we set up global values
     "renew-timer": 1000,
     "rebind-timer": 2000,
     "preferred-lifetime": 3000,
     "valid-lifetime": 4000,

 # Next we setup the interfaces to be used by the server.
     "interfaces-config": {
         "interfaces": [ "eth0" ]
     },

 # And we specify the type of a lease database
     "lease-database": {
         "type": "memfile",
         "persist": true,
         "name": "/var/kea/dhcp6.leases"
     },

 # Finally, we list the subnets from which we will be leasing addresses.
     "subnet6": [
         {
             "subnet": "2001:db8:1::/64",
             "pools": [
                  {
                      "pool": "2001:db8:1::1-2001:db8:1::ffff"
                  }
              ]
         }
     ]
 # DHCPv6 configuration ends with the next line
 }

 }

   The following paragraphs provide a brief overview of the parameters in the
   above example and their format. Subsequent sections of this chapter go
   into much greater detail for these and other parameters.

   The lines starting with a hash (#) are comments and are ignored by the
   server; they do not impact its operation in any way.

   The configuration starts in the first line with the initial opening curly
   bracket (or brace). Each configuration consists of one or more objects. In
   this specific example, we have only one object called Dhcp6. This is a
   simplified configuration, as usually there will be additional objects,
   like Logging or DhcpDns, but we omit them now for clarity. The Dhcp6
   configuration starts with the "Dhcp6": { line and ends with the
   corresponding closing brace (in the above example, the brace after the
   last comment). Everything defined between those lines is considered to be
   the Dhcp6 configuration.

   In the general case, the order in which those parameters appear does not
   matter. There are two caveats here though. The first one is to remember
   that the configuration file must be well formed JSON. That means that
   parameters for any given scope must be separated by a comma and there must
   not be a comma after the last parameter. When reordering a configuration
   file, keep in mind that moving a parameter to or from the last position in
   a given scope may require moving the comma as well. The second caveat is
   that it is uncommon -- although legal JSON -- to repeat the same parameter
   multiple times. If that happens, the last occurrence of a given parameter
   in a given scope is used while all previous instances are ignored. This is
   unlikely to cause any confusion as there are no real life reasons to keep
   multiple copies of the same parameter in your configuration file.

   Moving onto the DHCPv6 configuration elements, the very first few elements
   define some global parameters. valid-lifetime defines for how long the
   addresses (leases) given out by the server are valid. If nothing changes,
   a client that got an address is allowed to use it for 4000 seconds. (Note
   that integer numbers are specified as is, without any quotes around them.)
   The address will become deprecated in 3000 seconds (clients are allowed to
   keep old connections, but can't use this address for creating new
   connections). renew-timer and rebind-timer are values that define T1 and
   T2 timers that govern when the client will begin the renewal and rebind
   procedures.

   The interfaces-config map specifies the server configuration concerning
   the network interfaces, on which the server should listen to the DHCP
   messages. The interfaces parameter specifies a list of network interfaces
   on which the server should listen. Lists are opened and closed with square
   brackets, with elements separated by commas. Had we wanted to listen on
   two interfaces, the interfaces-config would look like this:

 "interfaces-config": {
     "interfaces": [ "eth0", "eth1" ]
 },

   The next couple of lines define the lease database, the place where the
   server stores its lease information. This particular example tells the
   server to use memfile, which is the simplest (and fastest) database
   backend. It uses an in-memory database and stores leases on disk in a CSV
   file. This is a very simple configuration. Usually, lease database
   configuration is more extensive and contains additional parameters. Note
   that lease-database is an object and opens up a new scope, using an
   opening brace. Its parameters (just one in this example -- type) follow.
   Had there been more than one, they would be separated by commas. This
   scope is closed with a closing brace. As more parameters follow, a
   trailing comma is present.

   Finally, we need to define a list of IPv6 subnets. This is the most
   important DHCPv6 configuration structure as the server uses that
   information to process clients' requests. It defines all subnets from
   which the server is expected to receive DHCP requests. The subnets are
   specified with the subnet6 parameter. It is a list, so it starts and ends
   with square brackets. Each subnet definition in the list has several
   attributes associated with it, so it is a structure and is opened and
   closed with braces. At minimum, a subnet definition has to have at least
   two parameters: subnet (that defines the whole subnet) and pool (which is
   a list of dynamically allocated pools that are governed by the DHCP
   server).

   The example contains a single subnet. Had more than one been defined,
   additional elements in the subnet6 parameter would be specified and
   separated by commas. For example, to define two subnets, the following
   syntax would be used:

 "subnet6": [
     {
         "pools": [
         {
             "pool": "2001:db8:1::/112"
         }
         ],
         "subnet": "2001:db8:1::/64"
     },
     {
         "pools": [ { "pool": "2001:db8:2::1-2001:db8:2::ffff" } ],
         "subnet": "2001:db8:2::/64",
         "interface": "eth0"
     }
 ]

   Note that indentation is optional and is used for aesthetic purposes only.
   In some cases in may be preferable to use more compact notation.

   After all parameters are specified, we have two contexts open: global and
   Dhcp6, hence we need two closing curly brackets to close them. In a real
   life configuration file there most likely would be additional components
   defined such as Logging or DhcpDdns, so the closing brace would be
   followed by a comma and another object definition.

  8.2.2. Lease Storage

   All leases issued by the server are stored in the lease database.
   Currently there are three database backends available: memfile (which is
   the default backend), MySQL and PostgreSQL.

    8.2.2.1. Memfile, Basic Storage for Leases

   The server is able to store lease data in different repositories. Larger
   deployments may elect to store leases in a database. Section 8.2.2.2,
   "Database Configuration" describes this option. In typical smaller
   deployments though, the server will use a CSV file rather than a database
   to store lease information. As well as requiring less administration, an
   advantage of using a file for storage is that it eliminates a dependency
   on third-party database software.

   The configuration of the file backend (Memfile) is controlled through the
   Dhcp6/lease-database parameters. The type parameter is mandatory and it
   specifies which storage for leases the server should use. The value of
   "memfile" indicates that the file should be used as the storage. The
   following list presents the remaining, not mandatory parameters, which can
   be used to configure the Memfile backend.

     o persist: controls whether the new leases and updates to existing
       leases are written to the file. It is strongly recommended that the
       value of this parameter is set to true at all times, during the
       server's normal operation. Not writing leases to disk will mean that
       if a server is restarted (e.g. after a power failure), it will not
       know what addresses have been assigned. As a result, it may hand out
       addresses to new clients that are already in use. The value of false
       is mostly useful for performance testing purposes. The default value
       of the persist parameter is true, which enables writing lease updates
       to the lease file.
     o name: specifies an absolute location of the lease file in which new
       leases and lease updates will be recorded. The default value for this
       parameter is "[kea-install-dir]/var/kea/kea-leases6.csv" .
     o lfc-interval: specifies the interval in seconds, at which the server
       (Memfile backend) will perform a lease file cleanup (LFC), which
       removes the redundant (historical) information from the lease file and
       effectively reduces the lease file size. The cleanup process is
       described in more detailed fashion further in this section. The
       default value of the lfc-interval is 0, which disables the LFC.

   The example configuration of the Memfile backend is presented below:

 "Dhcp6": {
     "lease-database": {
         "type": "memfile",
         "persist": true,
         "name": "/tmp/kea-leases6.csv",
         "lfc-interval": 1800
     }
 }

   It is important to know how the lease file contents are organized to
   understand why the periodic lease file cleanup is needed. Every time when
   the server updates a lease or creates a new lease for the client, the new
   lease information must be recorded in the lease file. For performance
   reasons, the server does not supersede the existing client's lease, as it
   would require the lookup of the specific lease entry, but simply appends
   the new lease information at the end of the lease file. The previous lease
   entries for the client are not removed. When the server loads leases from
   the lease file, e.g. at the server startup, it assumes that the latest
   lease entry for the client is the valid one. The previous entries are
   discarded. This means that the server can re-construct the accurate
   information about the leases even though there may be many lease entries
   for each client. However, storing many entries for each client results in
   bloated lease file and impairs the performance of the server's startup and
   reconfiguration, as it needs to process larger number of lease entries.

   The lease file cleanup removes all previous entries for each client and
   leaves only the latest ones. The interval at which the cleanup is
   performed is configurable, and it should be selected according to the
   frequency of lease renewals initiated by the clients. The more frequent
   renewals are, the lesser value of the lfc-interval should be. Note
   however, that the LFC takes time and thus it is possible (although
   unlikely) that new cleanup is started while the previous cleanup instance
   is still running, if the lfc-interval is too short. The server would
   recover from this by skipping the new cleanup when it detects that the
   previous cleanup is still in progress. But, this implies that the actual
   cleanups will be triggered more rarely than configured. Moreover,
   triggering a new cleanup adds an overhead to the server, which will not be
   able to respond to new requests for a short period of time when the new
   cleanup process is spawned. Therefore, it is recommended that the
   lfc-interval value is selected in a way that would allow for completing
   the cleanup before the new cleanup is triggered.

   The LFC is performed by a separate process (in background) to avoid
   performance impact on the server process. In order to avoid the conflicts
   between the two processes both using the same lease files, the LFC process
   operates on the copy of the original lease file, rather than on the lease
   file used by the server to record lease updates. There are also other
   files being created as a side effect of the lease file cleanup. The
   detailed description of the LFC is located on the Kea wiki:
   http://kea.isc.org/wiki/LFCDesign.

    8.2.2.2. Database Configuration

  Note

   Database access information must be configured for the DHCPv6 server, even
   if it has already been configured for the DHCPv4 server. The servers store
   their information independently, so each server can use a separate
   database or both servers can use the same database.

   Database configuration is controlled through the Dhcp6/lease-database
   parameters. The type of the database must be set to "mysql" or
   "postgresql", e.g.

 "Dhcp6": { "lease-database": { "type": "mysql", ... }, ... }

   Next, the name of the database is to hold the leases must be set: this is
   the name used when the lease database was created (see Section 4.3.2.1,
   "First Time Creation of Kea Database" or Section 4.3.3.1, "Manually Create
   the PostgreSQL Database and the Kea User").

 "Dhcp6": { "lease-database": { "name": "database-name" , ... }, ... }

   If the database is located on a different system than the DHCPv6 server,
   the database host name must also be specified (although it should be noted
   that this configuration may have a severe impact on server performance):

 "Dhcp6": { "lease-database": { "host": remote-host-name, ... }, ... }

   The usual state of affairs will be to have the database on the same
   machine as the DHCPv6 server. In this case, set the value to the empty
   string:

 "Dhcp6": { "lease-database": { "host" : "", ... }, ... }

   Finally, the credentials of the account under which the server will access
   the database should be set:

 "Dhcp6": { "lease-database": { "user": "user-name",
                                "password": "password",
                               ... },
            ... }

   If there is no password to the account, set the password to the empty
   string "". (This is also the default.)

  8.2.3. Interface selection

   The DHCPv6 server has to be configured to listen on specific network
   interfaces. The simplest network interface configuration instructs the
   server to listen on all available interfaces:

 "Dhcp6": {
     "interfaces-config": {
         "interfaces": [ "*" ]
     }
     ...
 }

   The asterisk plays the role of a wildcard and means "listen on all
   interfaces". However, it is usually a good idea to explicitly specify
   interface names:

 "Dhcp6": {
     "interfaces-config": {
         "interfaces": [ "eth1", "eth3" ]
     },
     ...
 }


   It is possible to use wildcard interface name (asterisk) concurrently with
   the actual interface names:

 "Dhcp6": {
     "interfaces-config": {
         "interfaces": [ "eth1", "eth3", "*" ]
     },
     ...
 }


   It is anticipated that this will form of usage only be used where it is
   desired to temporarily override a list of interface names and listen on
   all interfaces.

  8.2.4. IPv6 Subnet Identifier

   The subnet identifier is a unique number associated with a particular
   subnet. In principle, it is used to associate clients' leases with
   respective subnets. When the subnet identifier is not specified for a
   subnet being configured, it will be automatically assigned by the
   configuration mechanism. The identifiers are assigned from 1 and are
   monotonically increased for each subsequent subnet: 1, 2, 3 ....

   If there are multiple subnets configured with auto-generated identifiers
   and one of them is removed, the subnet identifiers may be renumbered. For
   example: if there are four subnets and the third is removed the last
   subnet will be assigned the identifier that the third subnet had before
   removal. As a result, the leases stored in the lease database for subnet 3
   are now associated with subnet 4, which may have unexpected consequences.
   In the future it is planned to implement a mechanism to preserve
   auto-generated subnet ids upon removal of one of the subnets. Currently,
   the only remedy for this issue is to manually specify a unique subnet
   identifier for each subnet.

   The following configuration will assign the specified subnet identifier to
   the newly configured subnet:

 "Dhcp6": {
     "subnet6": [
         {
             "subnet": "2001:db8:1::/64",
             "id": 1024,
             ...
         }
     ]
 }

   This identifier will not change for this subnet unless the "id" parameter
   is removed or set to 0. The value of 0 forces auto-generation of the
   subnet identifier.

  8.2.5. Unicast traffic support

   When the DHCPv6 server starts, by default it listens to the DHCP traffic
   sent to multicast address ff02::1:2 on each interface that it is
   configured to listen on (see Section 8.2.3, "Interface selection"). In
   some cases it is useful to configure a server to handle incoming traffic
   sent to the global unicast addresses as well. The most common reason for
   that is to have relays send their traffic to the server directly. To
   configure the server to listen on a specific unicast address, the notation
   to specify interfaces has been extended. An interface name can be
   optionally followed by a slash, followed by the global unicast address on
   which the server should listen. This will be done in addition to normal
   link-local binding + listening on ff02::1:2 address. The sample
   configuration below shows how to listen on 2001:db8::1 (a global address)
   configured on the eth1 interface.

 "Dhcp6": {
     "interfaces-config": {
         "interfaces": [ "eth1/2001:db8::1" ]
     },
     ...
 }


   This configuration will cause the server to listen on eth1 on link-local
   address, multicast group (ff02::1:2) and 2001:db8::1.

   It is possible to mix interface names, wildcards and interface
   name/addresses on the list of interfaces. It is not possible to specify
   more than one unicast address on a given interface.

   Care should be taken to specify proper unicast addresses. The server will
   attempt to bind to those addresses specified, without any additional
   checks. This approach is selected on purpose, so the software can be used
   to communicate over uncommon addresses if the administrator so desires.

  8.2.6. Subnet and Address Pool

   The essential role of a DHCPv6 server is address assignment. For this, the
   server has to be configured with at least one subnet and one pool of
   dynamic addresses to be managed. For example, assume that the server is
   connected to a network segment that uses the 2001:db8:1::/64 prefix. The
   Administrator of that network has decided that addresses from range
   2001:db8:1::1 to 2001:db8:1::ffff are going to be managed by the Dhcp6
   server. Such a configuration can be achieved in the following way:

 "Dhcp6": {
     "subnet6": [
        {
            "subnet": "2001:db8:1::/64",
            "pools": [
                {
                    "pool": "2001:db8:1::1-2001:db8:1::ffff"
                }
            ],
            ...
        }
     ]
 }

   Note that subnet is defined as a simple string, but the pool parameter is
   actually a list of pools: for this reason, the pool definition is enclosed
   in square brackets, even though only one range of addresses is specified.

   Each pool is a structure that contains the parameters that describe a
   single pool. Currently there is only one parameter, pool, which gives the
   range of addresses in the pool. Additional parameters will be added in
   future releases of Kea.

   It is possible to define more than one pool in a subnet: continuing the
   previous example, further assume that 2001:db8:1:0:5::/80 should also be
   managed by the server. It could be written as 2001:db8:1:0:5:: to
   2001:db8:1::5:ffff:ffff:ffff, but typing so many 'f's is cumbersome. It
   can be expressed more simply as 2001:db8:1:0:5::/80. Both formats are
   supported by Dhcp6 and can be mixed in the pool list. For example, one
   could define the following pools:

 "Dhcp6": {
     "subnet6": [
     {
         "subnet": "2001:db8:1::/64",
         "pools": [
             { "pool": "2001:db8:1::1-2001:db8:1::ffff" },
             { "pool": "2001:db8:1:05::/80" }
         ],
         ...
     }
     ]
 }

   The number of pools is not limited, but for performance reasons it is
   recommended to use as few as possible.

   The server may be configured to serve more than one subnet. To add a
   second subnet, use a command similar to the following:

 "Dhcp6": {
     "subnet6": [
     {
         "subnet": "2001:db8:1::/64",
         "pools": [
             { "pool": "2001:db8:1::1-2001:db8:1::ffff" }
         ]
     },
     {
         "subnet": "2001:db8:2::/64",
         "pools": [
             { "pool": "2001:db8:2::/64" }
         ]
     },

         ...
     ]
 }

   In this example, we allow the server to dynamically assign all addresses
   available in the whole subnet. Although rather wasteful, it is certainly a
   valid configuration to dedicate the whole /64 subnet for that purpose.
   Note that the Kea server does not preallocate the leases, so there is no
   danger in using gigantic address pools.

   When configuring a DHCPv6 server using prefix/length notation, please pay
   attention to the boundary values. When specifying that the server can use
   a given pool, it will also be able to allocate the first (typically
   network address) address from that pool. For example for pool
   2001:db8:2::/64 the 2001:db8:2:: address may be assigned as well. If you
   want to avoid this, use the "min-max" notation.

  8.2.7. Subnet and Prefix Delegation Pools

   Subnets may also be configured to delegate prefixes, as defined in RFC
   3633. A subnet may have one or more prefix delegation pools. Each pool has
   a prefixed address, which is specified as a prefix and a prefix length, as
   well as a delegated prefix length. delegated-len must not be shorter (that
   is it must be numerically greater or equal) than prefix-len. If both
   delegated-len and prefix-len are equal, the server will be able to
   delegate only one prefix. The delegated prefix does not have to match the
   subnet prefix.

   Below is a sample subnet configuration which enables prefix delegation for
   the subnet:

 "Dhcp6": {
     "subnet6": [
         {
             "subnet": "2001:d8b:1::/64",
             "pd-pools": [
                 {
                     "prefix": "3000:1::",
                     "prefix-len": 64,
                     "delegated-len": 96
                 }
             ]
         }
     ],
     ...
 }

  8.2.8. Standard DHCPv6 options

   One of the major features of a DHCPv6 server is to provide configuration
   options to clients. Although there are several options that require
   special behavior, most options are sent by the server only if the client
   explicitly requests them. The following example shows how to configure DNS
   servers, which is one of the most frequently used options. Numbers in the
   first column are added for easier reference and will not appear on screen.
   Options specified in this way are considered global and apply to all
   configured subnets.

 "Dhcp6": {
     "option-data": [
         {
            "name": "dns-servers",
            "code": 23,
            "space": "dhcp6",
            "csv-format": true,
            "data": "2001:db8::cafe, 2001:db8::babe"
         },
         ...
     ]
 }

   The option-data> line creates a new entry in the option-data table. This
   table contains information on all global options that the server is
   supposed to configure in all subnets. The name line specifies the option
   name. (For a complete list of currently supported names, see Table 8.1,
   "List of standard DHCPv6 options".) The next line specifies the option
   code, which must match one of the values from that list. The line
   beginning with space specifies the option space, which must always be set
   to "dhcp6" as these are standard DHCPv6 options. For other name spaces,
   including custom option spaces, see Section 8.2.11, "Nested DHCPv6 options
   (custom option spaces)". The next line specifies the format in which the
   data will be entered: use of CSV (comma separated values) is recommended.
   The data line gives the actual value to be sent to clients. Data is
   specified as normal text, with values separated by commas if more than one
   value is allowed.

   Options can also be configured as hexadecimal values. If "csv-format" is
   set to false, the option data must be specified as a string of hexadecimal
   numbers. The following commands configure the DNS-SERVERS option for all
   subnets with the following addresses: 2001:db8:1::cafe and
   2001:db8:1::babe.

 "Dhcp6": {
     "option-data": [
         {
            "name": "dns-servers",
            "code": 23,
            "space": "dhcp6",
            "csv-format": false,
            "data": "2001 0DB8 0001 0000 0000 0000 0000 CAFE
                     2001 0DB8 0001 0000 0000 0000 0000 BABE"
         },
         ...
     ]
 }

   The value for the setting of the "data" element is split across two lines
   in this document for clarity: when entering the command, the whole string
   should be entered on the same line. Care should be taken to use proper
   encoding when using hexadecimal format as Kea's ability to validate data
   correctness in hexadecimal is limited.

   Most of the parameters in the "option-data" structure are optional and can
   be omitted in some circumstances as discussed in the Section 8.2.12,
   "Unspecified parameters for DHCPv6 option configuration".

   It is possible to override options on a per-subnet basis. If clients
   connected to most of your subnets are expected to get the same values of a
   given option, you should use global options: you can then override
   specific values for a small number of subnets. On the other hand, if you
   use different values in each subnet, it does not make sense to specify
   global option values (Dhcp6/option-data), rather you should set only
   subnet-specific values (Dhcp6/subnet[X]/option-data[Y]).

   The following commands override the global DNS servers option for a
   particular subnet, setting a single DNS server with address 2001:db8:1::3.

 "Dhcp6": {
     "subnet6": [
         {
             "option-data": [
                 {
                     "name": "dns-servers",
                     "code": 23,
                     "space": "dhcp6",
                     "csv-format": true,
                     "data": "2001:db8:1::3"
                 },
                 ...
             ],
             ...
         },
         ...
     ],
     ...
 }

   The currently supported standard DHCPv6 options are listed in Table 8.1,
   "List of standard DHCPv6 options". The "Name" and "Code" are the values
   that should be used as a name in the option-data structures. "Type"
   designates the format of the data: the meanings of the various types is
   given in Table 7.3, "List of standard DHCP option types".

   Some options are designated as arrays, which means that more than one
   value is allowed in such an option. For example the option dns-servers
   allows the specification of more than one IPv6 address, allowing clients
   to obtain the addresses of multiple DNS servers.

   The Section 8.2.9, "Custom DHCPv6 options" describes the configuration
   syntax to create custom option definitions (formats). It is generally not
   allowed to create custom definitions for standard options, even if the
   definition being created matches the actual option format defined in the
   RFCs. There is an exception from this rule for standard options for which
   Kea does not provide a definition yet. In order to use such options, a
   server administrator must create a definition as described in
   Section 8.2.9, "Custom DHCPv6 options" in the 'dhcp6' option space. This
   definition should match the option format described in the relevant RFC
   but the configuration mechanism would allow any option format as it has no
   means to validate the format at the moment.

   Table 8.1. List of standard DHCPv6 options

   +---------------------------------------------------------+
   |           Name           | Code |     Type     | Array? |
   |--------------------------+------+--------------+--------|
   | preference               |  7   |    uint8     | false  |
   |--------------------------+------+--------------+--------|
   | sip-server-dns           |  21  |     fqdn     |  true  |
   |--------------------------+------+--------------+--------|
   | sip-server-addr          |  22  | ipv6-address |  true  |
   |--------------------------+------+--------------+--------|
   | dns-servers              |  23  | ipv6-address |  true  |
   |--------------------------+------+--------------+--------|
   | domain-search            |  24  |     fqdn     |  true  |
   |--------------------------+------+--------------+--------|
   | nis-servers              |  27  | ipv6-address |  true  |
   |--------------------------+------+--------------+--------|
   | nisp-servers             |  28  | ipv6-address |  true  |
   |--------------------------+------+--------------+--------|
   | nis-domain-name          |  29  |     fqdn     |  true  |
   |--------------------------+------+--------------+--------|
   | nisp-domain-name         |  30  |     fqdn     |  true  |
   |--------------------------+------+--------------+--------|
   | sntp-servers             |  31  | ipv6-address |  true  |
   |--------------------------+------+--------------+--------|
   | information-refresh-time |  32  |    uint32    | false  |
   |--------------------------+------+--------------+--------|
   | bcmcs-server-dns         |  33  |     fqdn     |  true  |
   |--------------------------+------+--------------+--------|
   | bcmcs-server-addr        |  34  | ipv6-address |  true  |
   |--------------------------+------+--------------+--------|
   | geoconf-civic            |  36  |    record    | false  |
   |--------------------------+------+--------------+--------|
   | remote-id                |  37  |    record    | false  |
   |--------------------------+------+--------------+--------|
   | subscriber-id            |  38  |    binary    | false  |
   |--------------------------+------+--------------+--------|
   | client-fqdn              |  39  |    record    | false  |
   |--------------------------+------+--------------+--------|
   | pana-agent               |  40  | ipv6-address |  true  |
   |--------------------------+------+--------------+--------|
   | new-posix-timezone       |  41  |    string    | false  |
   |--------------------------+------+--------------+--------|
   | new-tzdb-timezone        |  42  |    string    | false  |
   |--------------------------+------+--------------+--------|
   | ero                      |  43  |    uint16    |  true  |
   |--------------------------+------+--------------+--------|
   | lq-query                 |  44  |    record    | false  |
   |--------------------------+------+--------------+--------|
   | client-data              |  45  |    empty     | false  |
   |--------------------------+------+--------------+--------|
   | clt-time                 |  46  |    uint32    | false  |
   |--------------------------+------+--------------+--------|
   | lq-relay-data            |  47  |    record    | false  |
   |--------------------------+------+--------------+--------|
   | lq-client-link           |  48  | ipv6-address |  true  |
   |--------------------------+------+--------------+--------|
   | erp-local-domain-name    |  65  |     fqdn     | false  |
   |--------------------------+------+--------------+--------|
   | rsoo                     |  66  |    empty     | false  |
   |--------------------------+------+--------------+--------|
   | client-linklayer-addr    |  79  |    binary    | false  |
   +---------------------------------------------------------+

  8.2.9. Custom DHCPv6 options

   It is also possible to define options other than the standard ones. Assume
   that we want to define a new DHCPv6 option called "foo" which will have
   code 100 and will convey a single unsigned 32 bit integer value. We can
   define such an option by using the following commands:

 "Dhcp6": {
     "option-def": [
         {
             "name": "foo",
             "code": 100,
             "type": "uint32",
             "array": false,
             "record-types": "",
             "space": "dhcp6",
             "encapsulate": ""
         }, ...
     ],
     ...
 }

   The "false" value of the "array" parameter determines that the option does
   NOT comprise an array of "uint32" values but rather a single value. Two
   other parameters have been left blank: "record-types" and "encapsulate".
   The former specifies the comma separated list of option data fields if the
   option comprises a record of data fields. The "record-fields" value should
   be non-empty if the "type" is set to "record". Otherwise it must be left
   blank. The latter parameter specifies the name of the option space being
   encapsulated by the particular option. If the particular option does not
   encapsulate any option space it should be left blank. Note that the above
   set of comments define the format of the new option and do not set its
   values.

   Once the new option format is defined, its value is set in the same way as
   for a standard option. For example the following commands set a global
   value that applies to all subnets.

 "Dhcp6": {
     "option-data": [
         {
             "name": "foo",
             "code": 100,
             "space": "dhcp6",
             "csv-format": true,
             "data": "12345"
         }, ...
     ],
     ...
 }

   New options can take more complex forms than simple use of primitives
   (uint8, string, ipv6-address etc): it is possible to define an option
   comprising a number of existing primitives.

   Assume we want to define a new option that will consist of an IPv6
   address, followed by an unsigned 16 bit integer, followed by a boolean
   value, followed by a text string. Such an option could be defined in the
   following way:

 "Dhcp6": {
     "option-def": [
         {
             "name": "bar",
             "code": 101,
             "space": "dhcp6",
             "type": "record",
             "array": false,
             "record-types": "ipv4-address, uint16, boolean, string",
             "encapsulate": ""
         }, ...
     ],
     ...
 }

   The "type" is set to "record" to indicate that the option contains
   multiple values of different types. These types are given as a
   comma-separated list in the "record-types" field and should be those
   listed in Table 7.3, "List of standard DHCP option types".

   The values of the option are set as follows:

 "Dhcp6": {
     "option-data": [
         {
             "name": "bar",
             "space": "dhcp6",
             "code": 101,
             "csv-format": true,
             "data": "2001:db8:1::10, 123, false, Hello World"
         }
     ],
     ...
 }

   csv-format is set true to indicate that the data field comprises a
   command-separated list of values. The values in the "data" must correspond
   to the types set in the "record-types" field of the option definition.

  Note

   In the general case, boolean values are specified as true or false,
   without quotes. Some specific boolean parameters may accept also "true",
   "false", 0, 1, "0" and "1". Future Kea versions will accept all those
   values for all boolean parameters.

  8.2.10. DHCPv6 vendor specific options

   Currently there are three option spaces defined: dhcp4 (to be used in
   DHCPv4 daemon) and dhcp6 (for the DHCPv6 daemon); there is also
   vendor-opts-space, which is empty by default, but options can be defined
   in it. Those options are called vendor-specific information options. The
   following examples show how to define an option "foo" with code 1 that
   consists of an IPv6 address, an unsigned 16 bit integer and a string. The
   "foo" option is conveyed in a vendor specific information option. This
   option comprises a single uint32 value that is set to "12345". The
   sub-option "foo" follows the data field holding this value.

 "Dhcp6": {
     "option-def": [
         {
             "name": "foo",
             "code": 1,
             "space": "vendor-encapsulated-options-space",
             "type": "record",
             "array": false,
             "record-types": "ipv6-address, uint16, string",
             "encapsulates": ""
         }
     ],
     ...
 }

   (Note that the option space is set to vendor-opts-space.) Once the option
   format is defined, the next step is to define actual values for that
   option:

 "Dhcp6": {
     "option-data": [
         {
             "name": "foo",
             "space": "vendor-encapsulated-options-space",
             "code": 1,
             "csv-format": true,
             "data": "2001:db8:1::10, 123, Hello World"
         },
         ...
     ],
     ...
 }

   We should also define values for the vendor-opts, that will convey our
   option foo.

 "Dhcp6": {
     "option-data": [
         ...,
         {
             "name": "vendor-encapsulated-options",
             "space": "dhcp6",
             "code": 17,
             "csv-format": true,
             "data": "12345"
         }
     ],
     ...
 }

  8.2.11. Nested DHCPv6 options (custom option spaces)

   It is sometimes useful to define completely new option spaces. This is
   useful if the user wants his new option to convey sub-options that use a
   separate numbering scheme, for example sub-options with codes 1 and 2.
   Those option codes conflict with standard DHCPv6 options, so a separate
   option space must be defined.

   Note that it is not required to create a new option space when defining
   sub-options for a standard option because it is created by default if the
   standard option is meant to convey any sub-options (see Section 8.2.10,
   "DHCPv6 vendor specific options").

   Assume that we want to have a DHCPv6 option called "container" with code
   102 that conveys two sub-options with codes 1 and 2. First we need to
   define the new sub-options:

 "Dhcp6": {
     "option-def": [
         {
             "name": "subopt1",
             "code": 1,
             "space": "isc",
             "type": "ipv6-address",
             "record-types": "",
             "array": false,
             "encapsulate": ""
         },
         {
             "name": "subopt2",
             "code": 2,
             "space": "isc",
             "type": "string",
             "record-types": "",
             "array": false
             "encapsulate": ""
         }
     ],
     ...
 }

   Note that we have defined the options to belong to a new option space (in
   this case, "isc").

   The next step is to define a regular DHCPv6 option and specify that it
   should include options from the isc option space:

 "Dhcp6": {
     "option-def": [
         ...,
         {
             "name": "container",
             "code": 102,
             "space": "dhcp6",
             "type": "empty",
             "array": false,
             "record-types": "",
             "encapsulate": "isc"
         }
     ],
     ...
 }

   The name of the option space in which the sub-options are defined is set
   in the encapsulate field. The type field is set to empty which limits this
   option to only carrying data in sub-options.

   Finally, we can set values for the new options:

 "Dhcp6": {
     "option-data": [
         {
             "name": "subopt1",
             "space": "isc",
             "code": 1,
             "csv-format": true,
             "data": "2001:db8::abcd"
         },
         }
             "name": "subopt2",
             "space": "isc",
             "code": 2,
             "csv-format": true,
             "data": "Hello world"
         },
         {
             "name": "container",
             "space": "dhcp6",
             "code": 102,
             "csv-format": true,
             "data": ""
         }
     ],
     ...
 }

   Even though the "container" option does not carry any data except
   sub-options, the "data" field must be explicitly set to an empty value.
   This is required because in the current version of Kea, the default
   configuration values are not propagated to the configuration parsers: if
   the "data" is not set the parser will assume that this parameter is not
   specified and an error will be reported.

   Note that it is possible to create an option which carries some data in
   addition to the sub-options defined in the encapsulated option space. For
   example, if the "container" option from the previous example was required
   to carry an uint16 value as well as the sub-options, the "type" value
   would have to be set to "uint16" in the option definition. (Such an option
   would then have the following data structure: DHCP header, uint16 value,
   sub-options.) The value specified with the "data" parameter -- which
   should be a valid integer enclosed in quotes, e.g. "123" -- would then be
   assigned to the uint16 field in the "container" option.

  8.2.12. Unspecified parameters for DHCPv6 option configuration

   In many cases it is not required to specify all parameters for an option
   configuration and the default values can be used. However, it is important
   to understand the implications of not specifing some of them as it may
   result in configuration errors. The list below explains the behavior of
   the server when a particular parameter is not explicitly specified:

     o name - the server requires an option name or option code to identify
       an option. If this parameter is unspecified, the option code must be
       specified.
     o code - the server requires an option name or option code to identify
       an option. This parameter may be left unspecified if the name
       parameter is specified. However, this also requires that the
       particular option has its definition (it is either a standard option
       or an administrator created a definition for the option using an
       'option-def' structure), as the option definition associates an option
       with a particular name. It is possible to configure an option for
       which there is no definition (unspecified option format).
       Configuration of such options requires the use of option code.
     o space - if the option space is unspecified it will default to 'dhcp6'
       which is an option space holding DHCPv6 standard options.
     o data - if the option data is unspecified it defaults to an empty
       value. The empty value is mostly used for the options which have no
       payload (boolean options), but it is legal to specify empty values for
       some options which carry variable length data and which spec allows
       for the length of 0. For such options, the data parameter may be
       omitted in the configuration.
     o csv-format - if this value is not specified and the definition for the
       particular option exists, the server will assume that the option data
       is specified as a list of comma separated values to be assigned to
       individual fields of the DHCP option. If the definition does not exist
       for this option, the server will assume that the data parameter
       contains the option payload in the binary format (represented as a
       string of hexadecimal digits). Note that not specifying this parameter
       doesn't imply that it defaults to a fixed value, but the configuration
       data interpretation also depends on the presence of the option
       definition. An administrator must be aware if the definition for the
       particular option exists when this parameter is not specified. It is
       generally recommended to not specify this parameter only for the
       options for which the definition exists, e.g. standard options.
       Setting csv-format to an explicit value will cause the server to
       strictly check the format of the option data specified.

  8.2.13. IPv6 Subnet Selection

   The DHCPv6 server may receive requests from local (connected to the same
   subnet as the server) and remote (connecting via relays) clients. As the
   server may have many subnet configurations defined, it must select an
   appropriate subnet for a given request.

   The server can not assume which of the configured subnets are local. In
   IPv4 it is possible as there is a reasonable expectation that the server
   will have a (global) IPv4 address configured on the interface, and can use
   that information to detect whether a subnet is local or not. That
   assumption is not true in IPv6, the DHCPv6 server must be able to operate
   while only having link-local addresses. Therefore an optional "interface"
   parameter is available within a subnet definition to designate that a
   given subnet is local, i.e. reachable directly over the specified
   interface. For example the server that is intended to serve a local subnet
   over eth0 may be configured as follows:

 "Dhcp6": {
     "subnet6": [
         {
             "subnet": "2001:db8:beef::/48",
             "pools": [
                  {
                      "pool": "2001:db8:beef::/48"
                  }
              ],
             "interface": "eth0"
         }
     ],
     ...
 }

  8.2.14. DHCPv6 Relays

   A DHCPv6 server with multiple subnets defined must select the appropriate
   subnet when it receives a request from a client. For clients connected via
   relays, two mechanisms are used:

   The first uses the linkaddr field in the RELAY_FORW message. The name of
   this field is somewhat misleading in that it does not contain a link-layer
   address: instead, it holds an address (typically a global address) that is
   used to identify a link. The DHCPv6 server checks if the address belongs
   to a defined subnet and, if it does, that subnet is selected for the
   client's request.

   The second mechanism is based on interface-id options. While forwarding a
   client's message, relays may insert an interface-id option into the
   message that identifies the interface on the relay that received the
   message. (Some relays allow configuration of that parameter, but it is
   sometimes hardcoded and may range from the very simple (e.g. "vlan100") to
   the very cryptic: one example seen on real hardware was
   "ISAM144|299|ipv6|nt:vp:1:110"). The server can use this information to
   select the appropriate subnet. The information is also returned to the
   relay which then knows the interface to use to transmit the response to
   the client. In order for this to work successfully, the relay interface
   IDs must be unique within the network and the server configuration must
   match those values.

   When configuring the DHCPv6 server, it should be noted that two
   similarly-named parameters can be configured for a subnet:

     o "interface" defines which local network interface can be used to
       access a given subnet.
     o "interface-id" specifies the content of the interface-id option used
       by relays to identify the interface on the relay to which the response
       packet is sent.

   The two are mutually exclusive: a subnet cannot be both reachable locally
   (direct traffic) and via relays (remote traffic). Specifying both is a
   configuration error and the DHCPv6 server will refuse such a
   configuration.

   To specify interface-id with value "vlan123", the following commands can
   be used:

 "Dhcp6": {
     "subnet6": [
         {
             "subnet": "2001:db8:beef::/48",
             "pools": [
                  {
                      "pool": "2001:db8:beef::/48"
                  }
              ],
             "interface-id": "vlan123"
         }
     ],
     ...
 }

  8.2.15. Relay-Supplied Options

   RFC 6422 defines a mechanism called Relay-Supplied DHCP Options. In
   certain cases relay agents are the only entities that may have specific
   information. They can insert options when relaying messages from the
   client to the server. The server will then do certain checks and copy
   those options to the response that will be sent to the client.

   There are certain conditions that must be met for the option to be
   included. First, the server must not provide the option by itself. In
   other words, if both relay and server provide an option, the server always
   takes precedence. Second, the option must be RSOO-enabled. IANA mantains a
   list of RSOO-enabled options here. However, there may be cases when system
   administrators want to echo other options. Kea can be instructed to treat
   other options as RSOO-enabled. For example, to mark options 110, 120 and
   130 as RSOO-enabled, the following syntax should be used:

 "Dhcp6": {
     "relay-supplied-options": [ "110", "120", "130" ],
     ...
 }

   As of March 2015, only option 65 is RSOO-enabled by IANA. This option will
   always be treated as such and there's no need to explicitly mark it. Also,
   when enabling standard options, it is possible to use their names, rather
   than option code, e.g. (e.g. use dns-servers instead of 23). See
   Table 8.1, "List of standard DHCPv6 options" for the names. In certain
   cases it could also work for custom options, but due to the nature of the
   parser code this may be unreliable and should be avoided.

  8.2.16. Client Classification in DHCPv6

  Note

   DHCPv6 server has been extended to support limited client classification.
   Although the current capability is modest, it is expected to be expanded
   in the future. It is envisaged that the majority of client classification
   extensions will be using hooks extensions.

   In certain cases it is useful to differentiate between different types of
   clients and treat them differently. The process of doing classification is
   conducted in two steps. The first step is to assess an incoming packet and
   assign it to zero or more classes. This classification is currently
   simple, but is expected to grow in capability soon. Currently the server
   checks whether the incoming packet includes vendor class option (16). If
   it has, the content of that option is prepended with "VENDOR_CLASS_" then
   it is interpreted as a class. For example, modern cable modems will send
   this option with value "docsis3.0" and as a result the packet will belong
   to class "VENDOR_CLASS_docsis3.0".

   It is envisaged that the client classification will be used for changing
   behavior of almost any part of the DHCP engine processing, including
   assigning leases from different pools, assigning different option (or
   different values of the same options) etc. For now, there is only one
   mechanism that is taking advantage of client classification: subnet
   selection.

   Kea can be instructed to limit access to given subnets based on class
   information. This is particularly useful for cases where two types of
   devices share the same link and are expected to be served from two
   different subnets. The primary use case for such a scenario are cable
   networks. There are two classes of devices: the cable modem itself, which
   should be handed a lease from subnet A and all other devices behind modems
   that should get a lease from subnet B. That segregation is essential to
   prevent overly curious users from playing with their cable modems. For
   details on how to set up class restrictions on subnets, see
   Section 8.2.17, "Limiting access to IPv6 subnet to certain classes".

  8.2.17. Limiting access to IPv6 subnet to certain classes

   In certain cases it beneficial to restrict access to certain subnets only
   to clients that belong to a given class. For details on client classes,
   see Section 8.2.16, "Client Classification in DHCPv6". This is an
   extension of a previous example from Section 8.2.6, "Subnet and Address
   Pool". Let's assume that the server is connected to a network segment that
   uses the 2001:db8:1::/64 prefix. The Administrator of that network has
   decided that addresses from range 2001:db8:1::1 to 2001:db8:1::ffff are
   going to be managed by the Dhcp6 server. Only clients belonging to the
   eRouter1.0 client class are allowed to use that pool. Such a configuration
   can be achieved in the following way:

 "Dhcp6": {
     "subnet6": [
         {
             "subnet": "2001:db8:1::/64",
             "pools": [
                  {
                      "pool": "2001:db8:1::-2001:db8:1::ffff"
                  }
              ],
             "client-class": "VENDOR_CLASS_eRouter1.0"
         }
     ],
     ...
 }

   Care should be taken with client classification as it is easy for clients
   that do not meet class criteria to be denied any service altogether.

  8.2.18. Configuring DHCPv6 for DDNS

   As mentioned earlier, kea-dhcp6 can be configured to generate requests to
   the DHCP-DDNS server (referred to here as "D2") to update DNS entries.
   These requests are known as NameChangeRequests or NCRs. Each NCR contains
   the following information:

    1. Whether it is a request to add (update) or remove DNS entries

    2. Whether the change requests forward DNS updates (AAAA records),
       reverse DNS updates (PTR records), or both.

    3. The FQDN, lease address, and DHCID

   The parameters controlling the generation of NCRs for submission to D2 are
   contained in the "dhcp-ddns" section of kea-dhcp6 configuration. The
   mandatory parameters for the DHCP DDNS configuration are enable-updates
   which is unconditionally required, and qualifying-suffix which has no
   default value and is required when enable-updates is set to true. The two
   (disabled and enabled) minimal DHCP DDNS configurations are:

 "Dhcp6": {
     "dhcp-ddns": {
         "enable-updates": false
     },
     ...
 }

   and for example:

 "Dhcp6": {
     "dhcp-ddns": {
         "enable-updates": true,
         "qualifying-suffix": "example."
     },
     ...
 }

   The default values for the "dhcp-ddns" section are as follows:

     o "server-ip": "127.0.0.1"
     o "server-port": 53001
     o "sender-ip": ""
     o "sender-port": 0
     o "max-queue-size": 1024
     o "ncr-protocol": "UDP"
     o "ncr-format": "JSON"
     o "override-no-update": false
     o "override-client-update": false
     o "replace-client-name": false
     o "generated-prefix": "myhost"

    8.2.18.1. DHCP-DDNS Server Connectivity

   In order for NCRs to reach the D2 server, kea-dhcp6 must be able to
   communicate with it. kea-dhcp6 uses the following configuration parameters
   to control how it communications with D2:

     o enable-updates - determines whether or not kea-dhcp6 will generate
       NCRs. If missing, this value is assumed to be false hence DDNS updates
       are disabled. To enable DDNS updates set this value to true:
     o server-ip - IP address on which D2 listens for requests. The default
       is the local loopback interface at address 127.0.0.1. You may specify
       either an IPv4 or IPv6 address.
     o server-port - port on which D2 listens for requests. The default value
       is 53001.
     o sender-ip - IP address which kea-dhcp6 should use to send requests to
       D2. The default value is blank which instructs kea-dhcp6 to select a
       suitable address.
     o sender-port - port which kea-dhcp6 should use to send requests to D2.
       The default value of 0 instructs kea-dhcp6 to select a suitable port.
     o max-queue-size - maximum number of requests allowed to queue waiting
       to be sent to D2. This value guards against requests accumulating
       uncontrollably if they are being generated faster than they can be
       delivered. If the number of requests queued for transmission reaches
       this value, DDNS updating will be turned off until the queue backlog
       has been sufficiently reduced. The intent is to allow kea-dhcp6 to
       continue lease operations. The default value is 1024.
     o ncr-format - Socket protocol use when sending requests to D2.
       Currently only UDP is supported. TCP may be available in an upcoming
       release.
     o ncr-protocol - Packet format to use when sending requests to D2.
       Currently only JSON format is supported. Other formats may be
       available in future releases.

   By default, kea-dhcp-ddns is assumed to running on the same machine as
   kea-dhcp6, and all of the default values mentioned above should be
   sufficient. If, however, D2 has been configured to listen on a different
   address or port, these values must altered accordingly. For example, if D2
   has been configured to listen on 2001:db8::5 port 900, the following
   commands would be required:

 "Dhcp6": {
     "dhcp-ddns": {
         "server-ip": "2001:db8::5",
         "server-port": 900,
         ...
     },
     ...
 }

    8.2.18.2. When does kea-dhcp6 generate DDNS request

   kea-dhcp6 follows the behavior prescribed for DHCP servers in RFC 4704. It
   is important to keep in mind that kea-dhcp6 provides the initial decision
   making of when and what to update and forwards that information to D2 in
   the form of NCRs. Carrying out the actual DNS updates and dealing with
   such things as conflict resolution are the purview of D2 (Chapter 9, The
   DHCP-DDNS Server).

   This section describes when kea-dhcp6 will generate NCRs and the
   configuration parameters that can be used to influence this decision. It
   assumes that the "enable-updates" parameter is true.

  Note

   Currently the interface between kea-dhcp6 and D2 only supports requests
   which update DNS entries for a single IP address. If a lease grants more
   than one address, kea-dhcp6 will create the DDNS update request for only
   the first of these addresses. Support for multiple address mappings may be
   provided in a future release.

   In general, kea-dhcp6 will generate DDNS update requests when:

    1. A new lease is granted in response to a DHCP REQUEST

    2. An existing lease is renewed but the FQDN associated with it has
       changed.

    3. An existing lease is released in response to a DHCP RELEASE

   In the second case, lease renewal, two DDNS requests will be issued: one
   request to remove entries for the previous FQDN and a second request to
   add entries for the new FQDN. In the last case, a lease release, a single
   DDNS request to remove its entries will be made. The decision making
   involved when granting a new lease is more involved and is discussed next.

   kea-dhcp6 will generate a DDNS update request only if the DHCP REQUEST
   contains the FQDN option (code 39). By default kea-dhcp6 will respect the
   FQDN N and S flags specified by the client as shown in the following
   table:

   Table 8.2. Default FQDN Flag Behavior

   +------------------------------------------------------------------------+
   | Client    | Client Intent           | Server Response    | Server      |
   | Flags:N-S |                         |                    | Flags:N-S-O |
   |-----------+-------------------------+--------------------+-------------|
   |           | Client wants to do      | Server generates   |             |
   | 0-0       | forward updates, server | reverse-only       | 1-0-0       |
   |           | should do reverse       | request            |             |
   |           | updates                 |                    |             |
   |-----------+-------------------------+--------------------+-------------|
   |           | Server should do both   | Server generates   |             |
   | 0-1       | forward and reverse     | request to update  | 0-1-0       |
   |           | updates                 | both directions    |             |
   |-----------+-------------------------+--------------------+-------------|
   | 1-0       | Client wants no updates | Server does not    | 1-0-0       |
   |           | done                    | generate a request |             |
   +------------------------------------------------------------------------+

   The first row in the table above represents "client delegation". Here the
   DHCP client states that it intends to do the forward DNS updates and the
   server should do the reverse updates. By default, kea-dhcp6 will honor the
   client's wishes and generate a DDNS request to D2 to update only reverse
   DNS data. The parameter, "override-client-update", can be used to instruct
   the server to override client delegation requests. When this parameter is
   true, kea-dhcp6 will disregard requests for client delegation and generate
   a DDNS request to update both forward and reverse DNS data. In this case,
   the N-S-O flags in the server's response to the client will be 0-1-1
   respectively.

   (Note that the flag combination N=1, S=1 is prohibited according to RFC
   4702. If such a combination is received from the client, the packet will
   be dropped by kea-dhcp6.)

   To override client delegation, issue the following commands:

 "Dhcp6": {
     "dhcp-ddns": {
         "override-client-update": true,
         ...
     },
     ...
 }

   The third row in the table above describes the case in which the client
   requests that no DNS updates be done. The parameter, "override-no-update",
   can be used to instruct the server to disregard the client's wishes. When
   this parameter is true, kea-dhcp6 will generate DDNS update requests to
   kea-dhcp-ddns even if the client requests no updates be done. The N-S-O
   flags in the server's response to the client will be 0-1-1.

   To override client delegation, issue the following commands:

 "Dhcp6": {
     "dhcp-ddns": {
         "override-no-update": true,
         ...
     },
     ...
 }

    8.2.18.3. kea-dhcp6 name generation for DDNS update requests

   Each NameChangeRequest must of course include the fully qualified domain
   name whose DNS entries are to be affected. kea-dhcp6 can be configured to
   supply a portion or all of that name based upon what it receives from the
   client in the DHCP REQUEST.

   The rules for determining the FQDN option are as follows:

    1. If configured to do so ignore the REQUEST contents and generate a FQDN
       using a configurable prefix and suffix.

    2. Otherwise, using the domain name value from the client FQDN option as
       the candidate name:

         a. If the candidate name is a fully qualified domain name then use
            it.

         b. If the candidate name is a partial (i.e. unqualified) name then
            add a configurable suffix to the name and use the result as the
            FQDN.

         c. If the candidate name is a empty then generate a FQDN using a
            configurable prefix and suffix.

   To instruct kea-dhcp6 to always generate a FQDN, set the parameter
   "replace-client-name" to true:

 "Dhcp6": {
     "dhcp-ddns": {
         "replace-client-name": true,
         ...
     },
     ...
 }

   The prefix used when generating a FQDN is specified by the
   "generated-prefix" parameter. The default value is "myhost". To alter its
   value, simply set it to the desired string:

 "Dhcp6": {
     "dhcp-ddns": {
         "generated-prefix": "another.host",
         ...
     },
     ...
 }

   The suffix used when generating a FQDN or when qualifying a partial name
   is specified by the qualifying-suffix parameter. This parameter has no
   default value, thus it is mandatory when DDNS updates are enabled. To set
   its value simply set it to the desired string:

 "Dhcp6": {
     "dhcp-ddns": {
         "qualifying-suffix": "foo.example.org",
         ...
     },
     ...
 }

   When qualifying a partial name, kea-dhcp6 will construct a name with the
   format:

   [candidate-name].[qualifying-suffix].

   where candidate-name is the partial name supplied in the REQUEST. For
   example, if FQDN domain name value was "some-computer" and
   qualifying-suffix "example.com", the generated FQDN would be:

   some-computer.example.com.

   When generating the entire name, kea-dhcp6 will construct name of the
   format:

   [generated-prefix]-[address-text].[qualifying-suffix].

   where address-text is simply the lease IP address converted to a
   hyphenated string. For example, if lease address is 3001:1::70E, the
   qualifying suffix "example.com", and the default value is used for
   generated-prefix, the generated FQDN would be:

   myhost-3001-1--70E.example.com.

8.3. Host reservation in DHCPv6

   There are many cases where it is useful to provide a configuration on a
   per host basis. The most obvious one is to reserve specific, static IPv6
   address or/and prefix for exclusive use by a given client (host) -
   returning client will get the same address or/and prefix every time and
   other clients will never get that address. Note that there may be cases
   when the new reservation has been made for the client for the address or
   prefix being currently in use by another client. We call this situation a
   "conflict". The conflicts get resolved automatically over time as
   described in the subsequent sections. Once conflict is resolved, the
   client will keep receiving the reserved configuration when it renews.

   Another example when the host reservations are applicable is when a host
   that has specific requirements, e.g. a printer that needs additional DHCP
   options or a cable modem needs specific parameters. Yet another possible
   use case for host reservation is to define unique names for hosts.
   Although not all of the presented use cases are are implemented yet, Kea
   software will support them in the near future.

   Hosts reservations are defined as parameters for each subnet. Each host
   can be identified by either DUID or its hardware/MAC address. See
   Section 8.8, "MAC/Hardware addresses in DHCPv6" for details. There is an
   optional reservations array in the Subnet6 structure. Each element in that
   array is a structure, that holds information about a single host. In
   particular, such a structure has to have an indentifer that uniquely
   identifies a host. In DHCPv6 context, such an identifier is a hardware
   (MAC) address or a DUID. Also, either one or more addresses or prefixes
   should be specified. It is possible to specify a hostname. Additional
   capabilities are planned.

   The following example shows how to reserve addresses and prefixes for
   specific hosts:

 "subnet6": [
     {
         "subnet": "2001:db8:1::/48",
         "pools": [ { "pool": "2001:db8:1::/80" } ],
         "pd-pools": [
             {
                 "prefix": "2001:db8:1:8000::",
                 "prefix-len": 56,
                 "delegated-len": 64
             }
         ],
         "reservations": [
             {
                 "duid": "01:02:03:04:05:0A:0B:0C:0D:0E",
                 "ip-addresses": [ "2001:db8:1::100" ]
             },
             {
                 "hw-address": "00:01:02:03:04:05",
                 "ip-addresses": [ "2001:db8:1::101" ]
             },
             {
                 "duid": "01:02:03:04:05:06:07:08:09:0A",
                 "ip-addresses": [ "2001:db8:1::102" ],
                 "prefixes": [ "2001:db8:2:abcd::/64" ],
                 "hostname": "foo.example.com"
             }
         ]
     }
 ]

   This example makes 3 reservations. The first one reserves 2001:db8:1::100
   address for the client using DUID 01:02:03:04:05:0A:0B:0C:0D:0E. The
   second one also reserves an address, but does so using MAC or hardware
   address, rather than DUID. The third example is most advanced. It reserves
   an address, a prefix and a hostname at the same time.

   Note that DHCPv6 allows for a single client to lease multiple addresses
   and multiple prefixes at the same time. In the upcoming Kea releases, it
   will be possible to have multiple addresses and prefixes reserved for a
   single host. Therefore ip-addresses and prefixes are plural and are
   actually arrays. As of 0.9.1 having more than one IPv6 address or prefix
   is only partially supported.

   Making a reservation for a mobile host that may visit multiple subnets
   requires a separate host definition in each subnet it is expected to
   visit. It is not allowed to define multiple host definitions with the same
   hardware address in a single subnet. It is a valid configuration, if such
   definitions are specified in different subnets, though. The reservation
   for a given host should include only one identifier, either DUID or
   hwardware address. Defining both for the same host is considered a
   configuration error, but as of 0.9.1 beta, it is not rejected.

   Adding host reservation incurs a performance penalty. In principle, when
   the server that does not support host reservation responds to a query, it
   needs to check whether there is a lease for a given address being
   considered for allocation or renewal. The server that also supports host
   reservation, has to perform additional checks: not only if the address is
   currently used (if there is a lease for it), but also whether the address
   could be used by someone else (if there is a reservation for it). That
   additional check incurs performance penalty.

  8.3.1. Address/prefix reservation types

   In a typical scenario there's an IPv6 subnet defined with a certain part
   of it dedicated for dynamic address allocation by the DHCPv6 server. There
   may be an additional address space defined for prefix delegation. Those
   dynamic parts are referred to as dynamic pools, address and prefix pools
   or simply pools. In principle, the host reservation can reserve any
   address or prefix that belongs to the subnet. The reservations that
   specify an address that belongs to configured pools are called in-pool
   reservations. In contrast, those that do not belong to dynamic pools are
   called out-of-pool reservations. There is no formal difference in the
   reservation syntax. As of 0.9.1, both reservation types are handled
   uniformly. However, upcoming releases may offer improved performance if
   there are only out-of-pool reservations as the server will be able to skip
   reservation checks when dealing with existing leases. Therefore, system
   administrators are encouraged to use out-of-pool reservations, if
   possible.

  8.3.2. Conflicts in DHCPv6 reservations

   As reservations and lease information are stored in different places,
   conflicts may arrise. Consider the following series of events. The server
   has configured the dynamic pool of addresses from the range of
   2001:db8::10 to 2001:db8::20. Host A requests an address and gets
   2001:db8::10. Now the system administrator decides to reserve an address
   for host B. He decides to reserve 2001:db8::10 for that purpose. In
   general, reserving an address that is currently assigned to someone else
   is not recommended, but there are valid use cases where such an operation
   is warranted.

   The server now has a conflict to resolve. Let's analyze the situation
   here. If host B boots up and request an address, the server is not able to
   assign the reserved address 2001:db8::10. A naive approach would to be
   immediately remove the lease for host A and create a new one for host B.
   That would not solve the problem, though, because as soon as host B get
   the address, it will detect that the address is already in use by someone
   else (host A) and would send Decline. Therefore in this situation, the
   server has to temporarily assign a different address from the dynamic pool
   (not matching what has been reserved) to host B.

   When the host A renews its address, the server will discover that the
   address being renewed is now reserved for someone else (host B). Therefore
   the server will remove the lease for 2001:db8::10 and select a new address
   and will create a new lease for it. It will send two addresses in its
   response: the old address with lifetimes set to 0 to explicitly indicate
   that it is no longer valid and a new address with non-zero lifetimes. When
   the host B renews its temporarily assigned address, the server will detect
   that the existing lease does not match reservation, so it will release the
   current address host B has and will create a new lease matching the
   reservation. Similar as before, the server will send two addresses: the
   temporarily assigned one with zeroed lifetimes, and the new one that
   matches reservation with proper lifetimes set.

   This recovery will succeed, even if other hosts will attempt to get the
   reserved address. Had the host C requested address 2001:db8::10 after the
   reservation was made, the server will propose a different address.

   This recovery mechanism allows the server to fully recover from a case
   where reservations conflict with existing leases. This procedure takes
   time and will roughly take as long as renew-timer value specified. The
   best way to avoid such recovery is to not define new reservations that
   conflict with existing leases. Another recommendation is to use
   out-of-pool reservations. If the reserved address does not belong to a
   pool, there is no way that other clients could get this address (note that
   having multiple reservations for the same address is not allowed).

  8.3.3. Reserving a hostname

   When the reservation for the client includes the hostname , the server
   will assign this hostname to the client and send it back in the Client
   FQDN, if the client sent the FQDN option to the the server. The reserved
   hostname always takes precedence over the hostname supplied by the client
   (via the FQDN option) or the autogenerated (from the IPv6 address)
   hostname.

   The server qualifies the reserved hostname with the value of the
   qualifying-suffix parameter. For example, the following subnet
   configuration:

 "subnet6": [
     {
         "subnet": "2001:db8:1::/48",
         "pools": [ { "pool": "2001:db8:1::/80" } ],
         "reservations": [
             {
                 "duid": "01:02:03:04:05:0A:0B:0C:0D:0E",
                 "ip-addresses": [ "2001:db8:1::100" ]
                 "hostname": "alice-laptop"
             }
         ]
     }
 ],
 "dhcp-ddns": {
     "enable-updates": true,
     "qualifying-suffix": "example.isc.org."
 }

   will result in assigning the "alice-laptop.example.isc.org." hostname to
   the client using the DUID "01:02:03:04:05:0A:0B:0C:0D:0E". If the
   qualifying-suffix is not specified, the default (empty) value will be
   used, and in this case the value specified as a hostname will be treated
   as fully qualified name. Thus, by leaving the qualifying-suffix empty it
   is possible to qualify hostnames for the different clients with different
   domain names:

 "subnet6": [
     {
         "subnet": "2001:db8:1::/48",
         "pools": [ { "pool": "2001:db8:1::/80" } ],
         "reservations": [
             {
                 "duid": "01:02:03:04:05:0A:0B:0C:0D:0E",
                 "ip-addresses": [ "2001:db8:1::100" ]
                 "hostname": "mark-desktop.example.org."
             }
         ]
     }
 ],
 "dhcp-ddns": {
     "enable-updates": true,
 }

   will result in assigning the "mark-desktop.example.org." hostname to the
   client using the DUID "01:02:03:04:05:0A:0B:0C:0D:0E".

  8.3.4. Reserving specific options

   Currently it is not possible to specify options in host reservation. Such
   a feature will be added in the upcoming Kea releases.

  8.3.5. Fine Tuning IPv6 Host Reservation

  Note

   reservation-mode in the DHCPv6 server is implemented in Kea 0.9.1 beta,
   but has not been tested and is considered experimental.

   Host reservation capability introduces additional restrictions for the
   allocation engine during lease selection and renewal. In particular, three
   major checks are necessary. First, when selecting a new lease, it is not
   sufficient for a candidate lease to be not used by another DHCP client. It
   also must not be reserved for another client. Second, when renewing a
   lease, additional check must be performed whether the address being
   renewed is not reserved for another client. Finally, when a host renews an
   address or a prefix, the server has to check whether there's a reservation
   for this host, so the existing (dynamically allocated) address should be
   revoked and the reserved one be used instead.

   Some of those checks may be unnecessary in certain deployments. Not
   performing them may improve performance. The Kea server provides the
   reservation-mode configuration parameter to select the types of
   reservations allowed for the particular subnet. Each reservation type has
   different constraints for the checks to be performed by the server when
   allocating or renewing a lease for the client. Allowed values are:

     o all - enables all host reservation types. This is the default value.
       This setting is the safest and the most flexible. It allows in-pool
       and out-of-pool reservations. As all checks are conducted, it is also
       the slowest.
     o out-of-pool - allows only out of pool host reservations. With this
       setting in place, the server may assume that all host reservations are
       for addresses that do not belong to the dynamic pool. Therefore it can
       skip the reservation checks when dealing with in-pool addresses, thus
       improving performance. Do not use this mode if any of your
       reservations use in-pool address. Caution is advised when using this
       setting. Kea 0.9.1 does not sanity check the reservations against
       reservation-mode. Misconfiguration may cause problems.
     o disabled - host reservation support is disabled. As there are no
       reservations, the server will skip all checks. Any reservations
       defined will be completely ignored. As the checks are skipped, the
       server may operate faster in this mode.

   An example configuration that disables reservation looks like follows:

 "Dhcp6": {
     "subnet6": [
         {
         "subnet": "2001:db8:1::/64",
         "reservation-mode": "disabled",
         ...
         }
     ]
 }

8.4. Server Identifier in DHCPv6

   The DHCPv6 protocol uses a "server identifier" (also known as a DUID) for
   clients to be able to discriminate between several servers present on the
   same link. There are several types of DUIDs defined, but RFC 3315
   instructs servers to use DUID-LLT if possible. This format consists of a
   link-layer (MAC) address and a timestamp. When started for the first time,
   the DHCPv6 server will automatically generate such a DUID and store the
   chosen value to a file. That file is read by the server and the contained
   value used whenever the server is subsequently started.

   It is unlikely that this parameter should ever need to be changed.
   However, if such a need arises, stop the server, edit the file and restart
   the server. (The file is named kea-dhcp6-serverid and by default is stored
   in the "var" subdirectory of the directory in which Kea is installed. This
   can be changed when Kea is built by using "--localstatedir" on the
   "configure" command line.) The file is a text file that contains double
   digit hexadecimal values separated by colons. This format is similar to
   typical MAC address format. Spaces are ignored. No extra characters are
   allowed in this file.

8.5. Stateless DHCPv6 (Information-Request Message)

   Typically DHCPv6 is used to assign both addresses and options. These
   assignments (leases) have state that changes over time, hence their name,
   stateful. DHCPv6 also supports a stateless mode, where clients request
   configuration options only. This mode is considered lightweight from the
   server perspective, as it does not require any state tracking; hence its
   name.

   The Kea server supports stateless mode. Clients can send
   Information-Request messages and the server will send back answers with
   the requested options (providing the options are available in the server
   configuration). The server will attempt to use per-subnet options first.
   If that fails - for whatever reason - it will then try to provide options
   defined in the global scope.

   Stateless and stateful mode can be used together. No special configuration
   directives are required to handle this. Simply use the configuration for
   stateful clients and the stateless clients will get just options they
   requested.

   This usage of global options allows for an interesting case. It is
   possible to run a server that provides just options and no addresses or
   prefixes. If the options have the same value in each subnet, the
   configuration can define required options in the global scope and skip
   subnet definitions altogether. Here's a simple example of such a
   configuration:

 "Dhcp6": {
     "interfaces-config": {
         "interfaces": [ "ethX" ]
     },
     "option-data": [ {
         "name": "dns-servers",
         "data": "2001:db8::1, 2001:db8::2"
     } ],
     "lease-database": { "type": "memfile" }
  }

   This very simple configuration will provide DNS server information to all
   clients in the network, regardless of their location. Note the
   specification of the memfile lease database: this is required since, as of
   version 0.9.1, Kea requires a lease database to be specified even if it is
   not used.

8.6. Using specific relay agent for a subnet

   The relay has to have an interface connected to the link on which the
   clients are being configured. Typically the relay has a global IPv6
   address configured on the interface that belongs to the subnet from which
   the server will assign addresses. In the typical case, the server is able
   to use the IPv6 address inserted by the relay (in the link-addr field in
   RELAY-FORW message) to select the appropriate subnet.

   However, that is not always the case. The relay address may not match the
   subnet in certain deployments. This usually means that there is more than
   one subnet allocated for a given link. The two most common examples where
   this is the case are long lasting network renumbering (where both old and
   new address space is still being used) and a cable network. In a cable
   network both cable modems and the devices behind them are physically
   connected to the same link, yet they use distinct addressing. In such
   case, the DHCPv6 server needs additional information (like the value of
   interface-id option or IPv6 address inserted in the link-addr field in
   RELAY-FORW message) to properly select an appropriate subnet.

   The following example assumes that there is a subnet 2001:db8:1::/64 that
   is accessible via relay that uses 3000::1 as its IPv6 address. The server
   will be able to select this subnet for any incoming packets that came from
   a relay that has an address in 2001:db8:1::/64 subnet. It will also select
   that subnet for a relay with address 3000::1.

 "Dhcp6": {
     "subnet6": [
         {
             "subnet": "2001:db8:1::/64",
             "pools": [
                  {
                      "pool": "2001:db8:1::1-2001:db8:1::ffff"
                  }
              ],
              "relay": {
                  "ip-address": "3000::1"
              }
         }
     ]
 }

8.7. Segregating IPv6 clients in a cable network

   In certain cases, it is useful to mix relay address information,
   introduced in Section 8.6, "Using specific relay agent for a subnet" with
   client classification, explained in Section 8.2.17, "Limiting access to
   IPv6 subnet to certain classes". One specific example is a cable network,
   where typically modems get addresses from a different subnet than all
   devices connected behind them.

   Let's assume that there is one CMTS (Cable Modem Termination System) with
   one CM MAC (a physical link that modems are connected to). We want the
   modems to get addresses from the 3000::/64 subnet, while everything
   connected behind modems should get addresses from another subnet
   (2001:db8:1::/64). The CMTS that acts as a relay an uses address 3000::1.
   The following configuration can serve that configuration:

 "Dhcp6": {
     "subnet6": [
         {
             "subnet": "3000::/64",
             "pools": [
                 { "pool": "3000::2 - 3000::ffff" }
             ],
             "client-class": "VENDOR_CLASS_docsis3.0",
             "relay": {
                 "ip-address": "3000::1"
             }
         },

         {
             "subnet": "2001:db8:1::/64",
             "pools": [
                  {
                      "pool": "2001:db8:1::1-2001:db8:1::ffff"
                  }
              ],
              "relay": {
                  "ip-address": "3000::1"
              }
         }
     ]
 }

8.8. MAC/Hardware addresses in DHCPv6

   MAC/hardware addesses are available in DHCPv4 messages from the clients
   and administrators frequently use that information to perform certain
   tasks, like per host configuration, address reserveration for specific MAC
   addresses and other. Unfortunately, DHCPv6 protocol does not provide any
   completely reliable way to retrieve that information. To mitigate that
   issue a number of mechanisms have been implemented in Kea that attempt to
   gather that information. Each of those mechanisms works in certain cases,
   but may fail in other cases. Whether the mechanism works or not in the
   particular deployment is somewhat dependent on the network topology and
   the technologies used.

   Kea allows for configuration which of the supported methods should be used
   and in which order. This configuration may be considered a fine tuning of
   the DHCP deployment. In a typical deployment the default value of "any" is
   sufficient and there is no need to select specific methods. Changing the
   value of this parameter is the most useful in cases when an administrator
   wants to disable certain method, e.g. if the administrator trusts the
   network infrastructure more than the information provided by the clients
   themselves, the administrator may prefer information provided by the
   relays over that provided by the clients. The format of this parameter is
   as follows:

 "Dhcp6": {
     "mac-sources": [ "method1", "method2", "method3", ... ],

     "subnet6": [ ... ],

     ...
 }

   When not specified, a special value of any is used, which instructs the
   server to attempt to use all the methods in sequence and use value
   returned by the first one that succeeds.

   Supported methods are:

     o any - not an actual method, just a keyword that instructs Kea to try
       all other methods and use the first one that succeeds. This is the
       default operation if no mac-sources are defined.
     o raw - In principle, a DHCPv6 server could use raw sockets to receive
       incoming traffic and extract MAC/hardware address information. This is
       currently not implemented for DHCPv6 and this value has no effect.
     o duid - DHCPv6 uses DUID identifiers instead of MAC addresses. There
       are currently four DUID types defined, with two of them (DUID-LLT,
       which is the default one and DUID-LL) convey MAC address information.
       Although RFC3315 forbids it, it is possible to parse those DUIDs and
       extract necessary information from them. This method is not completely
       reliable, as clients may use other DUID types, namely DUID-EN or
       DUID-UUID.
     o ipv6-link-local - Another possible aquisition method comes from the
       source IPv6 address. In typical usage, clients are sending their
       packets from IPv6 link-local addresses. There's a good chance that
       those addresses are based on EUI-64, which contains MAC address. This
       method is not completely reliable, as clients may use other link-local
       address types. In particular, privacy extensions, defined in RFC4941,
       do not use MAC addresses. Also note that successful extraction
       requires that the address's u-bit must be set to 1 and its g-bit set
       to 0, indicating that it is an interface identifier as per RFC 2373,
       section 2.5.1.
     o client-link-addr-option - One extension defined to alleviate missing
       MAC issues is client link-layer address option, defined in RFC 6939.
       This is an option that is inserted by a relay and contains information
       about client's MAC address. This method requires a relay agent that
       supports the option and is configured to insert it. This method is
       useless for directly connected clients. This parameter can also be
       specified as rfc6939, which is an alias for client-link-addr-option.
     o remote-id - RFC 4649 defines remote-id option that is inserted by a
       relay agent. Depending on the relay agent configuration, the inserted
       option may convey client's MAC address information. This parameter can
       also be specified as rfc4649, which is an alias for remote-id.
     o subscriber-id - Another option that is somewhat similar to the
       previous one is subscriber-id, defined in RFC 4580. It is, too,
       inserted by a relay agent that is configured to insert it. This
       parameter can also be specified as rfc4580, which is an alias for
       subscriber-id. This method is currently not implemented.
     o docsis-cmts - Yet another possible source of MAC address information
       are DOCSIS options inserted by a CMTS that acts as a DHCPv6 relay
       agent in cable networks. This method attempts to extract MAC address
       information from suboption 1026 (cm mac) of the vendor specific option
       with vendor-id=4491. This vendor option is extracted from the
       relay-forward message, not the original client's message.
     o docsis-modem - Yet another possible source of MAC address information
       are DOCSIS options inserted by the cable modem itself. This method
       attempts to extract MAC address information from suboption 36 (device
       id) of the vendor specific option with vendor-id=4491. This vendor
       option is extracted from the original client's message, not from any
       relay options.

8.9. Supported DHCPv6 Standards

   The following standards are currently supported:

     o Dynamic Host Configuration Protocol for IPv6, RFC 3315: Supported
       messages are SOLICIT, ADVERTISE, REQUEST, RELEASE, RENEW, REBIND,
       INFORMATION-REQUEST, CONFIRM and REPLY.
     o IPv6 Prefix Options for Dynamic Host Configuration Protocol (DHCP)
       version 6, RFC 3633: Supported options are IA_PD and IA_PREFIX. Also
       supported is the status code NoPrefixAvail.
     o DNS Configuration options for Dynamic Host Configuration Protocol for
       IPv6 (DHCPv6), RFC 3646: Supported option is DNS_SERVERS.
     o The Dynamic Host Configuration Protocol for IPv6 (DHCPv6) Relay Agent
       Remote-ID Option, RFC 4649: REMOTE-ID option is supported.
     o The Dynamic Host Configuration Protocol for IPv6 (DHCPv6) Client Fully
       Qualified Domain Name (FQDN) Option, RFC 4704: Supported option is
       CLIENT_FQDN.
     o Relay-Supplied DHCP Options, RFC 6422: Full functionality is
       supported: OPTION_RSOO, ability of the server to echo back the
       options, checks whether an option is RSOO-enabled, ability to mark
       additional options as RSOO-enabled.
     o Client Link-Layer Address Option in DHCPv6, RFC 6939: Supported option
       is client link-layer address option.

8.10. DHCPv6 Server Limitations

   These are the current limitations and known problems with the DHCPv6
   server software. Most of them are reflections of the early stage of
   development and should be treated as "not implemented yet", rather than
   actual limitations.

     o On-line configuration has some limitations. Adding new subnets or
       modifying existing ones work, as is removing the last subnet from the
       list. However, removing non-last (e.g. removing subnet 1,2 or 3 if
       there are 4 subnets configured) will cause issues. The problem is
       caused by simplistic subnet-id assignment. The subnets are always
       numbered, starting from 1. That subnet-id is then used in leases that
       are stored in the lease database. Removing non-last subnet will cause
       the configuration information to mismatch data in the lease database.
       It is possible to manually update subnet-id fields in MySQL or
       PostgreSQL database, but it is awkward and error prone process. A
       better reconfiguration support is planned.

     o The server will allocate, renew or rebind a maximum of one lease for a
       particular IA option (IA_NA or IA_PD) sent by a client. RFC 3315 and
       RFC 3633 allow for multiple addresses or prefixes to be allocated for
       a single IA.
     o Temporary addresses are not supported.
     o Duplication report (DECLINE) and client reconfiguration (RECONFIGURE)
       are not yet supported.
     o The server doesn't act upon expired leases. In particular, when a
       lease expires, the server doesn't request removal of the DNS records
       associated with it.

Chapter 9. The DHCP-DDNS Server

   Table of Contents

   9.1. Starting and Stopping the DHCP-DDNS Server

   9.2. Configuring the DHCP-DDNS Server

                9.2.1. Global Server Parameters

                9.2.2. TSIG Key List

                9.2.3. Forward DDNS

                9.2.4. Reverse DDNS

                9.2.5. Example DHCP-DDNS Server Configuration

   9.3. DHCP-DDNS Server Limitations

   The DHCP-DDNS Server (kea-dhcp-ddns, known informally as D2) conducts the
   client side of the DDNS protocol (defined in RFC 2136) on behalf of the
   DHCPv4 and DHCPv6 servers (kea-dhcp4 and kea-dhcp6 respectively). The DHCP
   servers construct DDNS update requests, known as NameChangeRequests
   (NCRs), based upon DHCP lease change events and then post these to D2. D2
   attempts to match each such request to the appropriate DNS server(s) and
   carry out the necessary conversation with those servers to update the DNS
   data.

   In order to match a request to the appropriate DNS servers, D2 must have a
   catalog of servers from which to select. In fact, D2 has two such
   catalogs, one for forward DNS and one for reverse DNS; these catalogs are
   referred to as DDNS Domain Lists. Each list consists of one or more named
   DDNS Domains. Further, each DDNS Domain has a list of one or more DNS
   servers that publish the DNS data for that domain.

   When conducting forward domain matching, D2 will compare the FQDN in the
   request against the name of each forward DDNS Domain. The domain whose
   name matches the longest portion of the FQDN is considered the best match.
   For example, if the FQDN is "myhost.sample.example.com.", and there are
   two forward domains in the catalog: "sample.example.com." and
   "example.com.", the former is regarded as the best match. In some cases,
   it may not be possible to find a suitable match. Given the same two
   forward domains there would be no match for the FQDN, "bogus.net", so the
   request would be rejected. Finally, if there are no forward DDNS Domains
   defined, D2 will simply disregard the forward update portion of requests.

   When conducting reverse domain matching, D2 constructs a reverse FQDN from
   the lease address in the request and compare that against the name of each
   reverse DDNS Domain. Again, the domain whose name matches the longest
   portion of the FQDN is considered the best match. For instance, if the
   lease address is "172.16.1.40" and there are two reverse domains in the
   catalog: "1.16.172.in-addr.arpa." and "16.172.in-addr.arpa", the former is
   the best match. As with forward matching, it is possible to not find a
   suitable match. Given the same two domains, there would be no match for
   the lease address, "192.168.1.50", and the request would be rejected.
   Finally, if there are no reverse DDNS Domains defined, D2 will simply
   disregard the reverse update portion of requests.

9.1. Starting and Stopping the DHCP-DDNS Server

   kea-dhcp-ddns is the Kea DHCP-DDNS server and, due to the nature of DDNS,
   it is run alongside either the DHCPv4 or DHCPv6 components (or both). Like
   other parts of Kea, it is a separate binary that can be run on its own or
   through keactrl (see Chapter 6, Managing Kea with keactrl). In normal
   operation, controlling kea-dhcp-ddns with keactrl is recommended. However,
   it is also possible to run the DHCP-DDNS server directly. It accepts the
   following command-line switches:

     o -c file - specifies the configuration file. This is the only mandatory
       switch.
     o -d - specifies whether the server logging should be switched to
       debug/verbose mode. In verbose mode, the logging severity and
       debuglevel specified in the configuration file are ignored and "debug"
       severity and the maximum debuglevel (99) are assumed. The flag is
       convenient, for temporarily switching the server into maximum
       verbosity, e.g. when debugging.
     o -v - prints out Kea version and exits.
     o -V - prints out Kea extended version with additional parameters and
       exits.

   Upon start up the module will load its configuration and begin listening
   for NCRs based on that configuration.

9.2. Configuring the DHCP-DDNS Server

   Before starting kea-dhcp-ddns module for the first time, a configuration
   file needs to be created. The following default configuration is a
   template that can be customised to your requirements.

 "DhcpDdns": {
     "ip_address": "127.0.0.1",
     "port": 53001,
     "dns_server_timeout": 100,
     "ncr_protocol": "UDP",
     "ncr_format": "JSON",
     "tsig_keys": [ ],
     "forward_ddns": {
         "ddns_domains": [ ]
     },
     "reverse_ddns": {
         "ddns_domains": [ ]
     }
 }

   The configuration can be divided as follows, each of which is described in
   its own section:

     o Global Server Parameters - values which control connectivity and
       global server behavior
     o TSIG Key Info - defines the TSIG keys used for secure traffic with DNS
       servers
     o Forward DDNS - defines the catalog of Forward DDNS Domains
     o Reverse DDNS - defines the catalog of Forward DDNS Domains

  9.2.1. Global Server Parameters

     o ip_address - IP address on which D2 listens for requests. The default
       is the local loopback interface at address 127.0.0.1. You may specify
       either an IPv4 or IPv6 address.
     o port - Port on which D2 listens for requests. The default value is
       53001.
     o dns_server_timeout - The maximum amount of time in milliseconds, that
       D2 will wait for a response from a DNS server to a single DNS update
       message.
     o ncr_protocol - Packet format to use when sending requests to D2.
       Currently only JSON format is supported. Other formats may be
       available in future releases.
     o ncr_format - Socket protocol to use when sending requests to D2.
       Currently only UDP is supported. TCP may be available in an upcoming
       release.

   D2 must listen for change requests on a known address and port. By default
   it listens at 127.0.0.1 on port 53001. The following example illustrates
   how to change D2's global parameters so it will listen at 192.168.1.10
   port 900:

 "DhcpDdns": {
     "ip_address": "192.168.1.10",
     "port": 900,
     ...
     }
 }

  Warning

   It is possible for a malicious attacker to send bogus NameChangeRequests
   to the DHCP-DDNS server. Addresses other than the IPv4 or IPv6 loopback
   addresses (127.0.0.1 or ::1) should only be used for testing purposes, but
   note that local users may still communicate with the DHCP-DDNS server. A
   future version of Kea will implement authentication to guard against such
   attacks.

  Note

   If the ip_address and port are changed, it will be necessary to change the
   corresponding values in the DHCP servers' "dhcp-ddns" configuration
   section.

  9.2.2. TSIG Key List

   A DDNS protocol exchange can be conducted with or without TSIG (defined in
   RFC 2845). This configuration section allows the administrator to define
   the set of TSIG keys that may be used in such exchanges.

   To use TSIG when updating entries in a DNS Domain, a key must be defined
   in the TSIG Key List and referenced by name in that domain's configuration
   entry. When D2 matches a change request to a domain, it checks whether the
   domain has a TSIG key associated with it. If so, D2 will use that key to
   sign DNS update messages sent to and verify responses received from the
   domain's DNS server(s). For each TSIG key required by the DNS servers that
   D2 will be working with there must be a corresponding TSIG key in the TSIG
   Key list.

   As one might gather from the name, the tsig_key section of the D2
   configuration lists the TSIG keys. Each entry describes a TSIG key used by
   one or more DNS servers to authenticate requests and sign responses. Every
   entry in the list has three parameters:

     o name - a unique text label used to identify this key within the list.
       This value is used to specify which key (if any) should be used when
       updating a specific domain. So long as it is unique its content is
       arbitrary, although for clarity and ease of maintenance it is
       recommended that it match the name used on the DNS server(s). It
       cannot be blank.
     o algorithm - specifies which hashing algorithm should be used with this
       key. This value must specify the same algorithm used for the key on
       the DNS server(s). The supported algorithms are listed below:

          o HMAC-MD5
          o HMAC-SHA1
          o HMAC-SHA224
          o HMAC-SHA256
          o HMAC-SHA384
          o HMAC-SHA512

       This value is not case sensitive.
     o digest_bits - is used to specify the minimum truncated length in bits.
       The default value 0 means truncation is forbidden, not 0 values must
       be an integral number of octets, be greater than 80 and the half of
       the full length. Note in BIND9 this parameter is appended after a dash
       to the algorithm name.
     o secret - is used to specify the shared secret key code for this key.
       This value is case sensitive and must exactly match the value
       specified on the DNS server(s). It is a base64-encoded text value.

   As an example, suppose that a domain D2 will be updating is maintained by
   a BIND9 DNS server which requires dynamic updates to be secured with TSIG.
   Suppose further that the entry for the TSIG key in BIND9's named.conf file
   looks like this:

    :
    key "key.four.example.com." {
        algorithm hmac-sha224;
        secret "bZEG7Ow8OgAUPfLWV3aAUQ==";
    };
    :

   By default, the TSIG Key list is empty:

 "DhcpDdns": {
    "tsig_keys": [ ],
    ...
 }

   We must extend the list with a new key:

 "DhcpDdns": {
     "tsig_keys": [
         {
             "name": "key.four.example.com.",
             "algorithm": "HMAC-SHA224",
             "secret": "bZEG7Ow8OgAUPfLWV3aAUQ=="
         }
     ],
     ...
 }

   These steps would be repeated for each TSIG key needed. Note that the same
   TSIG key can be used with more than one domain.

  9.2.3. Forward DDNS

   The Forward DDNS section is used to configure D2's forward update
   behavior. Currently it contains a single parameter, the catalog of forward
   DDNS Domains, which is a list of structures.

 "DhcpDdns": {
     "forward_ddns": {
         "ddns_domains": [ ]
     },
     ...
 }

   By default, this list is empty, which will cause the server to ignore the
   forward update portions of requests.

    9.2.3.1. Adding Forward DDNS Domains

   A forward DDNS Domain maps a forward DNS zone to a set of DNS servers
   which maintain the forward DNS data (i.e. name to address mapping) for
   that zone. You will need one forward DDNS Domain for each zone you wish to
   service. It may very well be that some or all of your zones are maintained
   by the same servers. You will still need one DDNS Domain per zone.
   Remember that matching a request to the appropriate server(s) is done by
   zone and a DDNS Domain only defines a single zone.

   This section describes how to add Forward DDNS Domains. Repeat these steps
   for each Forward DDNS Domain desired. Each Forward DDNS Domain has the
   following parameters:

     o name - The fully qualified domain name (or zone) that this DDNS Domain
       can update. This is value used to compare against the request FQDN
       during forward matching. It must be unique within the catalog.
     o key_name - If TSIG is used with this domain's servers, this value
       should be the name of the key from within the TSIG Key List to use. If
       the value is blank (the default), TSIG will not be used in DDNS
       conversations with this domain's servers.
     o dns_servers - A list of one or more DNS servers which can conduct the
       server side of the DDNS protocol for this domain. The servers are used
       in a first to last preference. In other words, when D2 begins to
       process a request for this domain it will pick the first server in
       this list and attempt to communicate with it. If that attempt fails,
       it will move to next one in the list and so on until the it achieves
       success or the list is exhausted.

   To create a new forward DDNS Domain, one must add a new domain element and
   set its parameters:

 "DhcpDdns": {
     "forward_ddns": {
         "ddns_domains": [
             {
                 "name": "other.example.com.",
                 "key_name": "",
                 "dns_servers": [
                 ]
             }
         ]
     }
 }

   It is permissible to add a domain without any servers. If that domain
   should be matched to a request, however, the request will fail. In order
   to make the domain useful though, we must add at least one DNS server to
   it.

      9.2.3.1.1. Adding Forward DNS Servers

   This section describes how to add DNS servers to a Forward DDNS Domain.
   Repeat them for as many servers as desired for a each domain.

   Forward DNS Server entries represent actual DNS servers which support the
   server side of the DDNS protocol. Each Forward DNS Server has the
   following parameters:

     o hostname - The resolvable host name of the DNS server. This value is
       not yet implemented.
     o ip_address - The IP address at which the server listens for DDNS
       requests. This may be either an IPv4 or an IPv6 address.
     o port - The port on which the server listens for DDNS requests. It
       defaults to the standard DNS service port of 53.

   To create a new forward DNS Server, one must add a new server element to
   the domain and fill in its parameters. If for example the service is
   running at "172.88.99.10", then set it as follows:

 "DhcpDdns": {
     "forward_ddns": {
         "ddns_domains": [
             {
                 "name": "other.example.com.",
                 "key_name": "",
                 "dns_servers": [
                     {
                         "hostname": "",
                         "ip_address": "172.88.99.10",
                         "port": 53
                     }
                 ]
             }
         ]
     }
 }

  Note

   As stated earlier, "hostname" is not yet supported so, the parameter
   "ip_address" must be set to the address of the DNS server.

  9.2.4. Reverse DDNS

   The Reverse DDNS section is used to configure D2's reverse update
   behavior, and the concepts are the same as for the forward DDNS section.
   Currently it contains a single parameter, the catalog of reverse DDNS
   Domains, which is a list of structures.

 "DhcpDdns": {
     "reverse_ddns": {
         "ddns_domains": [ ]
     }
     ...
 }

   By default, this list is empty, which will cause the server to ignore the
   reverse update portions of requests.

    9.2.4.1. Adding Reverse DDNS Domains

   A reverse DDNS Domain maps a reverse DNS zone to a set of DNS servers
   which maintain the reverse DNS data (address to name mapping) for that
   zone. You will need one reverse DDNS Domain for each zone you wish to
   service. It may very well be that some or all of your zones are maintained
   by the same servers; even then, you will still need one DDNS Domain entry
   for each zone. Remember that matching a request to the appropriate
   server(s) is done by zone and a DDNS Domain only defines a single zone.

   This section describes how to add Reverse DDNS Domains. Repeat these steps
   for each Reverse DDNS Domain desired. Each Reverse DDNS Domain has the
   following parameters:

     o name - The fully qualified reverse zone that this DDNS Domain can
       update. This is the value used during reverse matching which will
       compare it with a reversed version of the request's lease address. The
       zone name should follow the appropriate standards: for example, to to
       support the IPv4 subnet 172.16.1, the name should be.
       "1.16.172.in-addr.arpa.". Similarly, to support an IPv6 subent of
       2001:db8:1, the name should be "1.0.0.0.8.B.D.0.1.0.0.2.ip6.arpa."
       Whatever the name, it must be unique within the catalog.
     o key_name - If TSIG should be used with this domain's servers, then
       this value should be the name of that key from the TSIG Key List. If
       the value is blank (the default), TSIG will not be used in DDNS
       conversations with this domain's servers. Currently this value is not
       used as TSIG has not been implemented.
     o dns_servers - a list of one or more DNS servers which can conduct the
       server side of the DDNS protocol for this domain. Currently the
       servers are used in a first to last preference. In other words, when
       D2 begins to process a request for this domain it will pick the first
       server in this list and attempt to communicate with it. If that
       attempt fails, it will move to next one in the list and so on until
       the it achieves success or the list is exhausted.

   To create a new reverse DDNS Domain, one must add a new domain element and
   set its parameters. For example, to support subnet 2001:db8:1::, the
   following configuration could be used:

 "DhcpDdns": {
     "reverse_ddns": {
         "ddns_domains": [
             {
                 "name": "1.0.0.0.8.B.D.0.1.0.0.2.ip6.arpa.",
                 "key_name": "",
                 "dns_servers": [
                 ]
             }
         ]
     }
 }

   It is permissible to add a domain without any servers. If that domain
   should be matched to a request, however, the request will fail. In order
   to make the domain useful though, we must add at least one DNS server to
   it.

      9.2.4.1.1. Adding Reverse DNS Servers

   This section describes how to add DNS servers to a Reverse DDNS Domain.
   Repeat them for as many servers as desired for each domain.

   Reverse DNS Server entries represents a actual DNS servers which support
   the server side of the DDNS protocol. Each Reverse DNS Server has the
   following parameters:

     o hostname - The resolvable host name of the DNS server. This value is
       currently ignored.
     o ip_address - The IP address at which the server listens for DDNS
       requests.
     o port - The port on which the server listens for DDNS requests. It
       defaults to the standard DNS service port of 53.

   To create a new reverse DNS Server, one must first add a new server
   element to the domain and fill in its parameters. If for example the
   service is running at "172.88.99.10", then set it as follows:

 "DhcpDdns": {
     "reverse_ddns": {
         "ddns_domains": [
             {
                 "name": "1.0.0.0.8.B.D.0.1.0.0.2.ip6.arpa.",
                 "key_name": "",
                 "dns_servers": [
                     {
                         "hostname": "",
                         "ip_address": "172.88.99.10",
                         "port": 53
                     }
                 ]
             }
         ]
     }
 }

  Note

   As stated earlier, "hostname" is not yet supported so, the parameter
   "ip_address" must be set to the address of the DNS server.

  9.2.5. Example DHCP-DDNS Server Configuration

   This section provides an example DHCP-DDNS server configuration based on a
   small example network. Let's suppose our example network has three
   domains, each with their own subnet.

   Table 9.1. Our example network

   +------------------------------------------------------------------------+
   | Domain           | Subnet          | Forward DNS Servers | Reverse DNS |
   |                  |                 |                     | Servers     |
   |------------------+-----------------+---------------------+-------------|
   | four.example.com | 192.0.2.0/24    | 172.16.1.5,         | 172.16.1.5, |
   |                  |                 | 172.16.2.5          | 172.16.2.5  |
   |------------------+-----------------+---------------------+-------------|
   | six.example.com  | 2001:db8:1::/64 | 3001:1::50          | 3001:1::51  |
   |------------------+-----------------+---------------------+-------------|
   | example.com      | 192.0.0.0/16    | 172.16.2.5          | 172.16.2.5  |
   +------------------------------------------------------------------------+

   We need to construct three forward DDNS Domains:

   Table 9.2. Forward DDNS Domains Needed

   +-------------------------------------------------+
   | #  | DDNS Domain Name  | DNS Servers            |
   |----+-------------------+------------------------|
   | 1. | four.example.com. | 172.16.1.5, 172.16.2.5 |
   |----+-------------------+------------------------|
   | 2. | six.example.com.  | 3001:1::50             |
   |----+-------------------+------------------------|
   | 3. | example.com.      | 172.16.2.5             |
   +-------------------------------------------------+

   As discussed earlier, FQDN to domain matching is based on the longest
   match. The FQDN, "myhost.four.example.com.", will match the first domain
   ("four.example.com") while "admin.example.com." will match the third
   domain ("example.com"). The FQDN, "other.example.net." will fail to match
   any domain and would be rejected.

   The following example configuration specified the Forward DDNS Domains.

 "DhcpDdns": {
     "forward_ddns": {
         "ddns_domains": [
             {
                 "name": "four.example.com.",
                 "key_name": "",
                 "dns_servers": [
                     { "ip_address": "172.16.1.5" },
                     { "ip_address": "172.16.2.5" }
                 ]
             },
             {
                 "name": "six.example.com.",
                 "key_name": "",
                 "dns_servers": [
                     { "ip_address": "2001:db8::1" }
                 ]
             },
             {
                 "name": "example.com.",
                 "key_name": "",
                 "dns_servers": [
                     { "ip_address": "172.16.2.5" }
                 ]
             },

         ]
     }
 }

   Similarly, we need to construct the three reverse DDNS Domains:

   Table 9.3. Reverse DDNS Domains Needed

   +-----------------------------------------------------------------+
   | #  | DDNS Domain Name                  | DNS Servers            |
   |----+-----------------------------------+------------------------|
   | 1. | 2.0.192.in-addr.arpa.             | 172.16.1.5, 172.16.2.5 |
   |----+-----------------------------------+------------------------|
   | 2. | 1.0.0.0.8.d.b.0.1.0.0.2.ip6.arpa. | 3001:1::50             |
   |----+-----------------------------------+------------------------|
   | 3. | 0.182.in-addr.arpa.               | 172.16.2.5             |
   +-----------------------------------------------------------------+

   An address of "192.0.2.150" will match the first domain, "2001:db8:1::10"
   will match the second domain, and "192.0.50.77" the third domain.

   These Reverse DDNS Domains are specified as follows:

 "DhcpDdns": {
     "reverse_ddns": {
         "ddns_domains": [
             {
                 "name": "2.0.192.in-addr.arpa.",
                 "key_name": "",
                 "dns_servers": [
                     { "ip_address": "172.16.1.5" },
                     { "ip_address": "172.16.2.5" }
                 ]
             }
             {
                 "name": "1.0.0.0.8.B.D.0.1.0.0.2.ip6.arpa.",
                 "key_name": "",
                 "dns_servers": [
                     { "ip_address": "2001:db8::1" }
                 ]
             }
             {
                 "name": "0.192.in-addr.arpa.",
                 "key_name": "",
                 "dns_servers": [
                     { "ip_address": "172.16.2.5" }
                 ]
             }
         ]
     }
 }

9.3. DHCP-DDNS Server Limitations

   The following are the current limitations of the DHCP-DDNS Server.

     o Requests received from the DHCP servers are placed in a queue until
       they are processed. Currently all queued requests are lost when the
       server shuts down.

Chapter 10. The LFC process

   Table of Contents

   10.1. Overview

   10.2. Command Line Options

10.1. Overview

   kea-lfc is a service process that removes redundant infomation from the
   files used to provide persistent storage for the memfile data base
   backend. This service is written to run as a stand alone process.

   While kea-lfc can be started externally, there is usually no need to do
   this. kea-lfc is run on a periodic basis by the Kea DHCP servers.

   The process operates on a set of files, using them for input and output of
   the lease entries and to indicate where it is in the process in case of an
   interruption. Currently the caller must supply names for all of the files,
   in the future this requirement may be relaxed with the process getting the
   names from either the config file or from defaults.

10.2. Command Line Options

   kea-lfc is run as follows:

 kea-lfc [-4 | -6] -c config-file -p pid-file -x previous-file -i copy-file -o output-file -f finish-file

   The argument -4 or -6 selects the protocol version of the lease files.

   The -c argument specifies the configuration file. This is required, but
   not currently used by the process.

   The -p argument specifies the PID file. When the kea-lfc process starts it
   attempts to determine if another instance of the process is already
   running by examining the pid file. If one is already running the new
   process is terminated. If one isn't running it writes its pid into the pid
   file.

   The other filenames specify where the kea-lfc process should look for
   input, write its output and use for bookkeeping.

     o previous -- When kea-lfc starts this is the result of any previous run
       of kea-lfc. When kea-lfc finishes it is the result of this run. If
       kea-lfc is interrupted before compelting this file may not exist.
     o input -- Before the DHCP server invokes kea-lfc it will move the
       current lease file here and then call kea-lfc with this file.
     o output -- The temporary file kea-lfc should use to write the leases.
       Upon completion of writing this this file it will be moved to the
       finish file (see below).
     o finish -- Another temporary file kea-lfc uses for bookkeeping. When
       kea-lfc completes writing the outputfile it moves it to this file
       name. After kea-lfc finishes deleting the other files (previous and
       input) it moves this file to previous lease file. By moving the files
       in this fashion the kea-lfc and the DHCP server processes can
       determine the correct file to use even if one of the processes was
       interrupted before completing its task.

   There are several additional arguments mostly for debugging purposes. -d
   Sets the logging level to debug. -v and -V print out version stamps with
   -V providing a longer form. -h prints out the usage string.

Chapter 11. Hooks Libraries

   Table of Contents

   11.1. Introduction

   11.2. Configuring Hooks Libraries

11.1. Introduction

   Although Kea offers a lot of flexibility, there may be cases where its
   behavior needs customisation. To accommodate this possibility, Kea
   includes the idea of "Hooks". This feature lets Kea load one or more
   dynamically-linked libraries (known as "hooks libraries") and, at various
   points in its processing ("hook points"), call functions in them. Those
   functions perform whatever custom processing is required.

   Hooks libraries are attached to individual Kea processes, not to Kea as a
   whole. This means (for example) that it is possible to associate one set
   of libraries with the DHCP4 server and a different set to the DHCP6
   server.

   Another point to note is that it is possible for a process to load
   multiple libraries. When processing reaches a hook point, Kea calls the
   hooks library functions attached to it. If multiple libraries have
   attached a function to a given hook point, Kea calls all of them, in the
   order in which the libraries are specified in the configuration file. The
   order may be important: consult the documentation of the libraries to see
   if this is the case.

   The next section describes how to configure hooks libraries. If you are
   interested in writing your own hooks library, information can be found in
   the Kea Developer's Guide.

11.2. Configuring Hooks Libraries

   The hooks libraries for a given process are configured using the
   hooks-libraries keyword in the configuration for that process. (Note that
   the word "hooks" is plural). The value of the keyword is an array of
   strings, each string corresponding to a hooks library. For example, to set
   up two hooks libraries for the DHCPv4 server, the configuration would be:

 "Dhcp4": {
     :
     "hooks-libraries": [
        "/opt/charging.so",
        "/opt/local/notification.so"
     ]
     :
 }

  Note

   At present, the libraries are specified as a simple list. A future version
   of Kea will support the capability of specifying a set of parameters for
   each library. When that is added, it is likely that the syntax for
   specifying hooks libraries will change.

   Notes:

     * The full path to each library should be given.

     * As noted above, order may be important - consult the documentation for
       each library.

     * An empty list has the same effect as omitting the hooks-libraries
       configuration element all together.

   At the present time, only the kea-dhcp4 and kea-dhcp6 processes support
   hooks libraries.

Chapter 12. libdhcp++ library

   Table of Contents

   12.1. Interface detection and Socket handling

   libdhcp++ is a common library written in C++ that handles many
   DHCP-related tasks, including:

     o DHCPv4 and DHCPv6 packets parsing, manipulation and assembly
     o Option parsing, manipulation and assembly
     o Network interface detection
     o Socket operations such as creation, data transmission and reception
       and socket closing.

   While this library is currently used by Kea, it is designed to be a
   portable, universal library, useful for any kind of DHCP-related software.

12.1. Interface detection and Socket handling

   Both the DHCPv4 and DHCPv6 components share network interface detection
   routines. Interface detection is currently supported on Linux, all BSD
   family (FreeBSD, NetBSD, OpenBSD), Mac OS X and Solaris 11 systems.

   DHCPv4 requires special raw socket processing to send and receive packets
   from hosts that do not have IPv4 address assigned yet. Support for this
   operation is implemented on Linux, FreeBSD, NetBSD and OpenBSD. It is
   likely that DHCPv4 component will not work in certain cases on other
   systems.

Chapter 13. Logging

   Table of Contents

   13.1. Logging Configuration

                13.1.1. Loggers

                13.1.2. Output Options

                13.1.3. Example Logger Configurations

   13.2. Logging Message Format

   13.3. Logging During Kea Startup

13.1. Logging Configuration

   During its operation Kea may produce many messages. They differ in
   severity (some are more important than others) and source (some are
   produced by specific components, e.g. hooks). It is useful to understand
   which log messages are needed and which are not and configure your logging
   appropriately. For example, debug level messages can be safely ignored in
   a typical deployment. They are, however, very useful when debugging a
   problem.

   The logging system in Kea is configured through the Logging structure in
   your configuration file. All daemons (e.g. DHCPv4 and DHCPv6 servers) will
   use the configuration in the Logging structure to see what should be
   logged and to where. This allows for sharing identical logging
   configuration between daemons.

  13.1.1. Loggers

   Within Kea, a message is logged through an entity called a "logger".
   Different parts of the code log messages through different loggers, and
   each logger can be configured independently of one another. For example
   there are different components that deal with hooks ("hooks" logger) and
   with DHCP engine ("dhcpsrv" logger).

   In the Logging structure in a configuration file you can specify the
   configuration for zero or more loggers. If there are no loggers specified,
   the code will use default values which cause Kea to log messages on at
   least INFO severity to standard output.

   The three most important elements of a logger configuration are the name
   (the component that is generating the messages), the severity (what to
   log), and the output_options (where to log).

    13.1.1.1. name (string)

   Each logger in the system has a name, the name being that of the component
   binary file using it to log messages. For instance, if you want to
   configure logging for the DHCPv4 server, you add an entry for a logger
   named "kea-dhcp4". This configuration will then be used by the loggers in
   the DHCPv4 server, and all the libraries used by it (unless a library
   defines its own logger and there is specific logger configuration that
   applies to that logger).

   If you want to specify logging for one specific library within a daemon,
   you set the name to daemon.library. For example, the logger used by the
   code from libdhcpsrv used in kea-dhcp4 binary has the full name of
   "kea-dhcp4.dhcpsrv". If there is no entry in Logging for a particular
   library, it will use the configuration given for the whole daemon.

   To illustrate this, suppose you want the dhcpsrv library to log messages
   of severity DEBUG, and the rest of the DHCPv4 server code to log messages
   of severity INFO. To achieve this you specify two loggers, one with the
   name "kea-dhcp4" and severity INFO, and one with the name
   "kea-dhcp4.dhcpsrv" with severity DEBUG. As there are no entries for other
   libraries, they will use the configuration for the daemon ("kea-dhcp4"),
   so giving the desired behavior.

   If there are multiple logger specifications in the configuration that
   might match a particular logger, the specification with the more specific
   logger name takes precedence. For example, if there are entries for both
   "kea-dhcp4" and "kea-dhcp4.dhcpsrv", the DHCPv4 server -- and all
   libraries it uses that are not dhcpsrv -- will log messages according to
   the configuration in the first entry ("kea-dhcp4").

   One final note about the naming. When specifying the daemon name within a
   logger, use the name of the binary file, e.g. "kea-dhcp4" for the DHCPv4
   server, "kea-dhcp6" for the DHCPv6 server, etc. When the message is
   logged, the message will include the name of the process (e.g.
   "kea-dhcp4") followed by the specific component in that process, e.g.
   "hooks". It is possible to specify either just the process name
   ("kea-dhcp4", will apply to everything logged within that process) or
   process name followed by specific logger, e.g. "kea-dhcp4.hooks". That
   will apply only to messages originating from that component.

   Currently defined loggers are:

     o kea-dhcp4 - this is the root logger for the DHCPv4 server. All
       components used by the DHCPv4 server inherit the settings from this
       logger if there is no specialized logger provided.
     o kea-dhcp4.dhcp4 - this is the logger used solely by the DHCPv4 server
       deamon. This logger does not specify logging settings for libraries
       used by the deamon.
     o kea-dhcp4.dhcpsrv - this logger is used by the libdhcpsrv library.
       This covers mostly DHCP engine (the lease allocation and renewal
       process), database operations and configuration.
     o kea-dhcp4.hooks - this logger is used during DHCPv4 hooks operation,
       i.e. anything related to user libraries will be logged using this
       logger.
     o kea-dhcp6 - this is the root logger for the DHCPv6 server. All
       components used by the DHCPv6 server inherit the settings from this
       logger if there is no specialized logger provided.
     o kea-dhcp6.dhcp6 - this is the logger used solely by the DHCPv6 server
       deamon. This logger does not specify logging settings for libraries
       used by the daemon.
     o kea-dhcp6.dhcpsrv - this logger is used by the libdhcpsrv library.
       This covers mostly DHCP engine (the lease allocation and renewal
       process), database operations and configuration.
     o kea-dhcp6.hooks - this logger is used during DHCPv6 hooks operation,
       i.e. anything related to user libraries will be logged using this
       logger.
     o kea-dhcp-ddns - this is the root logger for the kea-dhcp-ddns deamon.
       All components used by this deamon inherit the settings from this
       logger if there is no specialized logger provided.
     o kea-dhcp-ddns.dhcpddns - this is the logger used solely by the
       kea-dhcp-ddns deamon. This logger does not specify logging settings
       for libraries used by the deamon.

   Additional loggers may be defined in the future. The easiest way to find
   out the logger name is to configure all logging to go to a single
   destination and look for specific logger names. See Section 13.2, "Logging
   Message Format" for details.

    13.1.1.2. severity (string)

   This specifies the category of messages logged. Each message is logged
   with an associated severity which may be one of the following (in
   descending order of severity):

     o FATAL
     o ERROR
     o WARN
     o INFO
     o DEBUG

   When the severity of a logger is set to one of these values, it will only
   log messages of that severity, and the severities above it. The severity
   may also be set to NONE, in which case all messages from that logger are
   inhibited.

    13.1.1.3. output_options (list)

   Each logger can have zero or more output_options. These specify where log
   messages are sent. These are explained in detail below.

   The other options for a logger are:

    13.1.1.4. debuglevel (integer)

   When a logger's severity is set to DEBUG, this value specifies what debug
   messages should be printed. It ranges from 0 (least verbose) to 99 (most
   verbose).

   If severity for the logger is not DEBUG, this value is ignored.

  13.1.2. Output Options

   The main settings for an output option are the destination and a value
   called output, the meaning of which depends on the destination that is
   set.

    13.1.2.1. destination (string)

   The destination is the type of output. It can be one of:

     o console
     o file
     o syslog

    13.1.2.2. output (string)

   This value determines the type of output. There are several special values
   allowed here: stdout (messages are printed on standard output), stderr
   (messages are printed on stderr), syslog (messages are logged to syslog
   using default name, syslog:name (messages are logged to syslog using
   specified name). Any other value is interpreted as a filename that the
   logs should be written to.

   The other options for output_options are:

      13.1.2.2.1. maxsize (integer)

   Only relevant when destination is file, this is maximum file size of
   output files in bytes. When the maximum size is reached, the file is
   renamed and a new file opened. (For example, a ".1" is appended to the
   name -- if a ".1" file exists, it is renamed ".2", etc.)

   If this is 0, no maximum file size is used.

  Note

   Due to a limitation of the underlying logging library (log4cplus), rolling
   over the log files (from ".1" to ".2", etc) may show odd results: There
   can be multiple small files at the timing of roll over. This can happen
   when multiple processes try to roll over the files simultaneously. Version
   1.1.0 of log4cplus solved this problem, so if this or higher version of
   log4cplus is used to build Kea, it shouldn't happen. Even for older
   versions it is normally expected to happen rarely unless the log messages
   are produced very frequently by multiple different processes.

      13.1.2.2.2. maxver (integer)

   Maximum number of old log files to keep around when rolling the output
   file. Only relevant when output is "file".

  13.1.3. Example Logger Configurations

   In this example we want to set the global logging to write to the console
   using standard output.

 "Logging": {
     "loggers": [
         {
             "name": "kea-dhcp4",
             "output_options": [
                 {
                     "output": "stdout"
                 }
             ],
             "severity": "WARN"
         }
     ]
 }


   In this second example, we want to store debug log messages in a file that
   is at most 2MB and keep up to 8 copies of old logfiles. Once the logfile
   grows to 2MB, it will be renamed and a new file file be created.

 "Logging": {
     "loggers": [
         {
             "name": "kea-dhcp6",
             "output_options": [
                 {
                     "output": "/var/log/kea-debug.log",
                     "maxver": 8,
                     "maxsize": 204800,
                     "destination": "file"
                 }
             ],
             "severity": "DEBUG",
             "debuglevel": 99
         }
    ]
 }

13.2. Logging Message Format

   Each message written to the configured logging destinations comprises a
   number of components that identify the origin of the message and, if the
   message indicates a problem, information about the problem that may be
   useful in fixing it.

   Consider the message below logged to a file:

 2014-04-11 12:58:01.005 INFO  [kea-dhcp4.dhcpsrv/27456]
     DHCPSRV_MEMFILE_DB opening memory file lease database: type=memfile universe=4

   Note: the layout of messages written to the system logging file (syslog)
   may be slightly different. This message has been split across two lines
   here for display reasons; in the logging file, it will appear on one line.

   The log message comprises a number of components:

   2014-04-11 12:58:01.005

           The date and time at which the message was generated.

   INFO

           The severity of the message.

   [kea-dhcp4.dhcpsrv/27456]

           The source of the message. This comprises two elements: the Kea
           process generating the message (in this case, kea-dhcp4) and the
           component within the program from which the message originated
           (which is the name of the common library used by DHCP server
           implementations). The number after the slash is a process id
           (pid).

   DHCPSRV_MEMFILE_DB

           The message identification. Every message in Kea has a unique
           identification, which can be used as an index into the Kea
           Messages Manual (http://kea.isc.org/docs/kea-messages.html) from
           which more information can be obtained.

   opening memory file lease database: type=memfile universe=4

           A brief description. Within this text, information relating to the
           condition that caused the message to be logged will be included.
           In this example, the information is logged that the in-memory
           lease database backend will be used to store DHCP leases.

13.3. Logging During Kea Startup

   The logging configuration is specified in the configuration file. However,
   when Kea starts, the file is not read until some way into the
   initialization process. Prior to that, the logging settings are set to
   default values, although it is possible to modify some aspects of the
   settings by means of environment variables. Note that in the absence of
   any logging configuration in the configuration file, the settings of
   (possibly modified) default configuration will persist while the program
   is running.

   The following environment variables can be used to control the behavio of
   logging during startup:

   KEA_LOCKFILE_DIR

           Specifies a directory where the logging system should create its
           lock file. If not specified, it is prefix/var/run/kea, where
           prefix defaults to /usr/local. This variable must not end with a
           slash. There is one special value: "none", which instructs Kea to
           not create lock file at all. This may cause issues if several
           processes log to the same file.

   KEA_LOGGER_DESTINATION

           Specifies logging output. There are several special values.

                stdout

                        Log to standard output.

                stderr

                        Log to standard error.

                syslog[:fac]

                        Log via syslog. The optional fac (which is separated
                        from the word "syslog" by a colon) specifies the
                        facility to be used for the log messages. Unless
                        specified, messages will be logged using the facility
                        "local0".

           Any other value is treated as a name of the output file. If not
           specified otherwise, Kea will log to standard output.

Chapter 14. Acknowledgements

   Kea is primarily designed, developed, and maintained by Internet Systems
   Consortium, Inc. It is an open source project and contributions are
   welcomed.

   Support for the development of the DHCPv4, DHCPv6 and DHCP-DDNS components
   was provided by Comcast.

   Kea was initially implemented as a collection of applications within the
   BIND 10 framework. Hence, Kea development would not be possible without
   the generous support of past BIND 10 project sponsors.

   JPRS and CIRA were Patron Level BIND 10 sponsors.

   AFNIC, CNNIC, CZ.NIC, DENIC eG, Google, RIPE NCC, Registro.br, .nz
   Registry Services, and Technical Center of Internet were past BIND 10
   sponsors.

   Afilias, IIS.SE, Nominet, and SIDN were founding sponsors of the BIND 10
   project.
