IS-IS Support For The Power Conserving Path Placement Strategy (PCPPS)

Introduction introduces a Power Conserving Path Placement Strategy (PCPPS). When possible, PCPPS concentrates traffic onto a small set of network resources. When traffic is concentrated onto a small set of network resources, other network resources become idle and can be powered down until they are needed again. This conserves energy and reduces environmental impact. PCPPS uses information that is distributed by an IGP. This document specifies the IS-IS encoding for that information.

Conventions and Definitions The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 when, and only when, they appear in all capitals, as shown here.

Terminology The following terms are used in this document and defined in :

Power Group
Power Savings Potential (PSP)
Power-sleep-capable
Sleep status, AWAKE and ASLEEP
Sleeping adjacency
Sleeping bandwidth

Link State Database (LSDB) Elements

The Power Group TLV Power Groups are described in . The Power Group TLV is a top-level TLV. It carries a sequnce of 12-octet Power Group Entries. If a Power Group is Power-sleep-capable, it is advertised in Power Group TLV. Otherwise, it is not advertised in a Power Group TLV.

Power Group TLV depicts the Power Group TLV where:

Type: 1 octet, value TBD1
Length: 1 octet, unsigned integer. The length of the TLV, measured in octets, not including the type and length fields. The Length field MUST be a non-zero multiple of 12 octets.
Power Group Entries: A sequence of Power Group Entries as depicted in .

Power Group Entry Where:

Power Group Identifier: 4 octets. Identifies the Power Group. MUST NOT be equal to 0.
PSP: 4 octets, unsigned integer. The Power Group's PSP, in milliwatts. A value of 0 is valid.
Parent Identifier: 4 octets. A reference to the Power Group's parent.

The Power Group Identifier and Parent Identifier have node-local significance. They are interpreted only in the context of the originating Intermediate System. If the Parent Identifier is equal to 0, the Power Group has no parent (i.e., it is the root of a Power Group hierarchy). If the Parent Identifier is greater than 0 but cannot be resolved, the Power Group is processed as if it were the root of a Power Group hierarchy. If the complete current LSP set originated by one Intermediate System at one IS-IS level contains multiple Power Group entries with the same Power Group Identifier, and all such entries have identical PSP and Parent Identifier values, the receiver MUST treat them as a single advertisement. If entries with the same Power Group Identifier have different PSP or Parent Identifier values, the receiver MUST ignore all entries with that Power Group Identifier from that originator and level. The Power Group hierarchy MUST NOT contain a cycle. A Power Group whose Parent Identifier is equal to its own Power Group Identifier is a self-parenting cycle. A set of two or more Power Groups forms a cycle when following a Parent Identifier from any member eventually returns to that member. The receiver MUST ignore every Power Group that is a member of a cycle and MUST NOT use those Power Groups for path computation. These rules apply across all LSP fragments and all occurrences of the Power Group TLV in the current LSP set. Normal IS-IS LSP sequence-number, lifetime, purge, and LSP-set processing determines which LSP set is current. An originator SHOULD update all LSP fragments containing a changed Power Group advertisement as an atomic flooding operation where possible. During convergence, a receiver that observes conflicting entries MUST treat the affected Power Group as invalid rather than use potentially inconsistent PSP or hierarchy information.

The Sleeping Adjacencies TLV The Sleeping Adjacencies TLV is a top-level TLV.

Sleeping Adjacencies TLV Where:

Type: 1 octet, value TBD2
Length: 1 octet, unsigned integer. The length of the TLV, measured in octets, not including the type and length fields.
Sleeping Adjacencies: A sequence of complete IS-IS TLVs, also called embedded TLVs. The permitted embedded TLV types are 2, 22, 23, 222 and 223. Each embedded TLV is encoded using its normal Type, Length, and Value fields, as specified for that TLV when advertised outside the Sleeping Adjacencies TLV.

Implementations MUST ignore an embedded TLV whose type is not listed above. An embedded TLV can carry sub-TLVs and this document adds no new restrictions upon which sub-TLVs it can carry. An embedded TLV MUST fit entirely within the containing Sleeping Adjacencies TLV; it MUST NOT extend into another TLV. If an embedded TLV is truncated or has an invalid length, the receiver MUST ignore the entire Sleeping Adjacencies TLV. A sender MAY include more than one Sleeping Adjacencies TLV in an LSP when the all embedded TLVs do not fit in a single Sleeping Adjacencies TLV. A receiver MUST process the embedded TLVs in all Sleeping Adjacencies TLVs carried by the complete current LSP set as one set. If an adjacency is advertised both as sleeping and as non-sleeping in the complete current LSP set, the sleeping state MUST be retained and the adjacency MUST be treated as sleeping. If the node at the other end of a sleeping adjacency resets, some fields in the sleeping adjacency may become unresolvable. An implementation MAY retain such an advertisement, but it MUST NOT use an unresolvable field for path computation. The fields become usable when the remote node advertises the adjacency again, either as sleeping or as non-sleeping. These rules apply across all LSP fragments and all occurrences of the Sleeping Adjacencies TLV. Normal IS-IS LSP sequence-number, lifetime, purge, and LSP-set processing determines which LSP set is current. An originator SHOULD update all LSP fragments containing a changed Sleeping Adjacencies advertisement as an atomic flooding operation where possible.

Interface Extensions The following sub-TLVs are found in TLV 22, Extended IS Reachability, and TLV 222, MT-IS Reachability. Within those top-level TLVs, they are found in sub-TLVs that advertise interface information. This document defines these interface extensions for the single IS-IS topology and for multi-topology IS-IS reachability. They are not defined for TLV 23 (IS Neighbors) or TLV 223 (MT-IS Neighbor Attribute). These sub-TLVs represent layer-3 interfaces. When they represent a LAG, they represent a layer-3 abstraction that contains all LAG members.

The Power Group Member Sub-TLV This sub-TLV maps an interface to one or more Power Groups. A LAG can map to multiple Power Groups. However, this sub-TLV does not identify the LAG member through which the interface maps to each Power Group.

Power Group Member Sub-TLV depicts the Power Group Member Sub-TLV where:

Type: 1 octet, value TBD3
Length: 1 octet, unsigned integer. The length of the sub-TLV, measured in octets, not including the type and length fields. The length MUST be a non-zero multiple of 4.
Power Group Identifiers: A sequence of 4-octet unsigned integers. The number of identifiers is Length divided by 4. A Power Group Identifier MUST NOT be equal to 0.

If a Power Group Identifier cannot be resolved, it is ignored.

The Interface PSP Sub-TLV This sub-TLV advertises an interface's PSP.

Interface PSP Sub-TLV depicts the Interface PSP Sub-TLV where:

Type: 1 octet, value TBD4
Length: 1 octet, unsigned integer. MUST be 4. If the Length is not 4, the receiver MUST ignore the instance.
PSP: 4 octets, unsigned integer. The interface's PSP, in milliwatts.

Unidirectional Sleeping Bandwidth Sub-TLV This sub-TLV is applicable only to LAG interfaces and then only when the LAG interface is not sleeping. It MUST NOT be originated for a non-LAG link. A receiver MUST ignore this sub-TLV when it is advertised for a non-LAG interface.

Unidirectional Sleeping Bandwidth Sub-TLV depicts the Unidirectional Sleeping Bandwidth Sub-TLV where:

Type: 1 octet, value TBD5
Length: 1 octet, unsigned integer. MUST be 4. If the Length is not 4, the receiver MUST ignore the instance.
Sleeping Bandwidth: 4 octets, IEEE 754 binary32 floating-point value in network byte order, measured in bytes per second. NaN, positive infinity, negative infinity, and negative values are invalid. A receiver MUST ignore an instance containing an invalid value.

The Sleeping Bandwidth field carries the sleeping bandwidth of a LAG interface. It is the sum of the sleeping bandwidths of the LAG's component links. A component link's sleeping bandwidth is the amount of its maximum bandwidth that has been transitioned to power-sleep, excluding bandwidth currently allocated to RSVP-TE label switched paths. The value MUST NOT be advertised for a non-LAG link. For each interface, an implementation SHOULD originate at most one instance of each sub-TLV defined in this section. If multiple instances of the same sub-TLV are received for one interface and their values are identical, the receiver MUST treat them as one instance. If their values differ, the receiver MUST ignore all instances of that sub-TLV for that interface and MUST NOT select one based on sub-TLV order, LSP fragment number, arrival order, or processing order.

The Power-Sleep Capable Bit The Power-Sleep Capable flag (TBD6) is carried in the 16-bit Link-attributes sub-TLV (19) defined in . When set, this flag indicates that the link may be put into power-sleep mode. When clear, the link may not be put into power-sleep mode.

Security Considerations The information defined in this document is used by path-computation systems and may influence whether network resources are placed into power-sleep mode. An attacker that can inject, modify, replay, or suppress IS-IS advertisements could advertise false Power Group identifiers, PSP values, parent relationships, sleep states, sleeping bandwidth, or power-sleep capability. False advertisements could cause traffic to be concentrated on insufficient capacity, cause a sleeping resource to be selected, prevent eligible resources from being powered down, or cause repeated and unnecessary power-state transitions. False parent relationships could also alter the computed Power Group hierarchy and the resulting path selection. Implementations MUST validate received values according to the procedures in this document and MUST NOT use malformed, unresolvable, or otherwise invalid values for path computation. Implementations and operators SHOULD use the IS-IS authentication mechanisms appropriate for the deployment to protect these advertisements from unauthorized modification and injection. IS-IS authentication does not by itself prevent an authorized but misconfigured router from originating incorrect information; therefore, access to the control plane and configuration of power-management parameters should be restricted to trusted systems and operators. Implementations MUST apply normal IS-IS LSP sequence-number, lifetime, purge, and withdrawal processing to the TLVs defined in this document. Power Group and Sleeping Adjacencies information MUST NOT be retained after the originating LSP set is no longer valid. During LSP convergence, implementations MUST follow the conflict-handling rules in this document and MUST avoid using information that is ambiguous or invalid. Implementations SHOULD provide operational visibility into rejected, conflicting, expired, and otherwise invalid advertisements. A deployment should also ensure that the PCPPS or other path-computation component applies independent capacity and reachability checks before placing traffic on paths that rely on sleeping-bandwidth or power-sleep information.

IANA Considerations IANA is requested to add the following entries to the IS-IS Top-Level TLV Codepoints registry (https://www.iana.org/assignments/isis-tlv-codepoints/isis-tlv-codepoints.xhtml#tlv-codepoints): IS-IS Top-Level TLV Codepoints

Value	Name	IIH	LSP	SNP	Purge	MP	Status Reference
TBD1	Power Group	N	Y	N	N	N	This document
TBD2	Sleeping Adjacencies	N	Y	N	N	Y	This document

IANA is also requested to add the following entries to the IS-IS Sub-TLVs for TLVs Advertising Neighbor Information registry (https://www.iana.org/assignments/isis-tlv-codepoints/isis-tlv-codepoints.xhtml#isis-tlv-codepoints-advertising-neighbor-information): IS-IS Sub-TLVs for TLVs Advertising Neighbor Information

Type	Description	22	23	25	141	222	223	MP	Reference
TBD3	Power Group Member	Y	Y	N	N	Y	Y	N	This document
TBD4	Interface PSP	Y	Y	N	N	Y	Y	N	This document
TBD5	Unidirectional Sleeping Bandwidth (LAG only)	Y	Y	N	N	Y	Y	N	This document

IANA is also requested to add the following entry to the IS-IS Neighbor Link-Attribute Bit Values registry (https://www.iana.org/assignments/isis-tlv-codepoints/isis-tlv-codepoints.xhtml#isis-tlv-codepoints-19of22): IS-IS Neighbor Link-Attribute Bit Values

Value	Name	L2BM	Reference
TBD6	Power-Sleep Capable (requested bit value 0x0008)	N	This document

Acknowledgements Thanks to Les Ginsberg for his review and comments.