Appendix D. BIND 9 DNS Library Support
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# BIND 9 DNS Library Support

This version of BIND 9 "exports" its internal libraries so that they can be used by third-party applications more easily (we call them "export" libraries in this document). Certain library functions are altered from specific BIND-only behavior to more generic behavior when used by other applications; to enable this generic behavior, the calling program initializes the libraries by calling isc_lib_register().

In addition to DNS-related APIs that are used within BIND 9, the libraries provide the following features:

- The "DNS client" module. This is a higher-level API that provides an interface to name resolution, single DNS transaction with a particular server, and dynamic update. Regarding name resolution, it supports advanced features such as DNSSEC validation and caching. This module supports both synchronous and asynchronous mode.

- The "IRS" (Information Retrieval System) library. It provides an interface to parse the traditional `resolv.conf` file and more advanced, DNS-specific configuration file for the rest of this package (see the description for the `dns.conf` file below).

- As part of the IRS library, the standard address-name mapping functions, getaddrinfo() and getnameinfo(), are provided. They use the DNSSEC-aware validating resolver backend, and could use other advanced features of the BIND 9 libraries such as caching. The getaddrinfo() function resolves both A and AAAA RRs concurrently when the address family is unspecified.

- An experimental framework to support other event libraries than BIND 9's internal event task system.

### Installation

    $ make install

Normal installation of BIND also installs library object and header files. Root privilege is normally required.

To see how to build a custom application after the installation, see `lib/samples/Makefile-postinstall.in`.

### Known Defects/Restrictions

- The "fixed" RRset order is not (currently) supported in the export library. To use "fixed" RRset order for, e.g., named while still building the export library even without the fixed-order support, build them separately:

      $ ./configure --enable-fixed-rrset [other flags, but not --enable-exportlib]
      $ make
      $ ./configure --enable-exportlib [other flags, but not --enable-fixed-rrset]
      $ cd lib/export
      $ make

- RFC 5011 is not supported in the validating stub resolver of the export library. In fact, it is not clear whether it should be: trust anchors would be a system-wide configuration which would be managed by an administrator, while the stub resolver is used by ordinary applications run by a normal user.

- Not all common `/etc/resolv.conf` options are supported in the IRS library. The only available options in this version are debug and ndots.

### The dns.conf File

The IRS library supports an "advanced" configuration file related to the DNS library, for configuration parameters that would be beyond the capability of the `resolv.conf` file. Specifically, it is intended to provide DNSSEC-related configuration parameters. By default the path to this configuration file is `/etc/dns.conf`. This module is very experimental and the configuration syntax or library interfaces may change in future versions. Currently, only the trusted-keys statement is supported, whose syntax is the same as the same statement in `named.conf`. (See the section called “trusted-keys Statement Grammar” for details.)

### Sample Applications

Some sample application programs using this API are provided for reference. The following is a brief description of these applications.

#### sample: a simple stub resolver utility

This sends a query of a given name (of a given optional RR type) to a specified recursive server and prints the result as a list of RRs. It can also act as a validating stub resolver if a trust anchor is given via a set of command-line options.

Usage: sample [options] server_address hostname

Options and Arguments:

-t RRtype

  specifies the RR type of the query. The default is the A RR.

[-a algorithm] [-e] -k keyname -K keystring

  specifies a command-line DNS key to validate the answer. For example, to specify the following DNSKEY of example.com:

  example.com. 3600 IN DNSKEY 257 3 5 xxx

  specify the options as follows:

      -e -k example.com -K "xxx"

  -e means that this key is a zone's "key signing key" (also known as "secure entry point"). When -a is omitted rsasha1 is used by default.

-s domain:alt_server_address

  specifies a separate recursive server address for the specific "domain". Example: -s example.com:2001:db8::1234

server_address

  is an IP(v4/v6) address of the recursive server to which queries are sent.

hostname

  is the domain name for the query

#### sample-async: a simple stub resolver, working asynchronously

This is similar to "sample", but accepts a list of (query) domain names as a separate file and resolves the names asynchronously.

Usage: sample-async [-s server_address] [-t RR_type] input_file

Options and Arguments:

-s server_address
  is an IPv4 address of the recursive server to which queries are sent. (IPv6 addresses are not supported in this implementation.)
-t RR_type
  specifies the RR type of the queries. The default is the A RR.
input_file
  is a list of domain names to be resolved; each line consists of a single domain name. For example:

  www.example.com
  mx.example.net
  ns.xxx.example

#### sample-request: a simple DNS transaction client

sends a query to a specified server, and prints the response with minimal processing. It does not act as a "stub resolver": it stops the processing once it gets any response from the server, whether it's a referral or an alias (CNAME or DNAME) that would require further queries to get the ultimate answer. In other words, this utility acts as a very simplified dig.

Usage: sample-request [-t RRtype] server_address hostname

Options and Arguments:

-t RRtype

  specifies the RR type of the queries. The default is the A RR.

server_address

  is an IP(v4/v6) address of the recursive server to which the query is sent.

hostname

  is the domain name for the query

#### sample-gai: getaddrinfo() and getnameinfo() test code

is a test program to check getaddrinfo() and getnameinfo() behavior. It takes a host name as an argument, calls getaddrinfo() with the given host name, and calls getnameinfo() with the resulting IP addresses returned by getaddrinfo(). If the dns.conf file exists and defines a trust anchor, the underlying resolver acts as a validating resolver, and getaddrinfo()/getnameinfo() fails with an EAI_INSECUREDATA error when DNSSEC validation fails.

Usage: sample-gai hostname

#### sample-update: a simple dynamic update client program

accepts a single update command as a command-line argument, sends an update request message to the authoritative server, and shows the response from the server. In other words, this is a simplified nsupdate.

Usage: sample-update [options] (add|delete) "update data"

Options and Arguments:

-a auth_server

  is an IP address of the authoritative server that has authority for the zone containing the update name. This should normally be the primary authoritative server that accepts dynamic updates. It can also be a secondary server that is configured to forward update requests to the primary server.

-k keyfile

  is a TSIG key file to secure the update transaction. The keyfile format is the same as that for the nsupdate utility.

-p prerequisite

  is a prerequisite for the update; only one prerequisite can be specified. The prerequisite format is the same as that accepted by the nsupdate utility.

-r recursive_server

  is an IP address of a recursive server that this utility uses. A recursive server may be necessary to identify the authoritative server address to which the update request is sent.

-z zonename

  is the domain name of the zone that it contains.

(add|delete)

  specifies the type of update operation. Either "add" or "delete" must be specified.

"update data"

  specifies the data to be updated. A typical example of the data looks like "name TTL RRtype RDATA".

### Note

In practice, either -a or -r must be specified. Others can be optional; the underlying library routine tries to identify the appropriate server and the zone name for the update.

Examples: assuming the primary authoritative server of the dynamic.example.com zone has an IPv6 address 2001:db8::1234,

    $ sample-update -a sample-update -k Kxxx.+nnn+mmmm.key add "foo.dynamic.example.com 30 IN A 192.168.2.1"

adds an A RR for foo.dynamic.example.com using the given key.

    $ sample-update -a sample-update -k Kxxx.+nnn+mmmm.key delete "foo.dynamic.example.com 30 IN A"

removes all A RRs for foo.dynamic.example.com using the given key.

    $ sample-update -a sample-update -k Kxxx.+nnn+mmmm.key delete "foo.dynamic.example.com"

removes all RRs for foo.dynamic.example.com using the given key.

#### nsprobe: domain/name server checker in terms of RFC 4074

checks a set of domains to ensure the name servers of the domains behave correctly in terms of RFC 4074. This is included in the set of sample programs to show how the export library can be used in a DNS-related application.

Usage: nsprobe [-d] [-v [-v...]] [-c cache_address] [input_file]

Options

-d

  runs in "debug" mode. With this option, nsprobe dumps every RR it receives.

-v

  increases verbosity of other normal log messages. This can be specified multiple times.

-c cache_address

  specifies an IP address of a recursive (caching) name server. nsprobe uses this server to get the NS RRset of each domain and the A and/or AAAA RRsets for the name servers. The default value is 127.0.0.1.

input_file

  is a file name containing a list of domain (zone) names to be probed. when omitted the standard input is used. Each line of the input file specifies a single domain name, such as "example.com". In general, this domain name must be the apex name of some DNS zone, unlike normal "host names" such as "www.example.com". nsprobe first identifies the NS RRsets for the given domain name, and sends A and AAAA queries to these servers for some widely used names under the zone; specifically, adding "www" and "ftp" to the zone name.

### Library References

As of this writing, there is no formal "manual" for the libraries, except this document, header files (some of which provide pretty detailed explanations), and sample application programs.

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BIND 9.11.27 (Extended Support Version)