rfc-5330

A Link-Type sub-TLV to Convey the Number of Traffic Engineering Label Switched Paths Signalled with Zero Reserved Bandwidth across a Link

JP. Vasseur (Editor), M. Meyer, K. Kumaki, A. Bonda

date2008-10 streamIETF areartg wgmpls statusPROPOSED STANDARD pages8 canonicalhttps://www.rfc-editor.org/rfc/rfc5330 doi10.17487/RFC5330

Several Link-type sub-Type-Length-Values (sub-TLVs) have been defined for Open Shortest Path First (OSPF) and Intermediate System to Intermediate System (IS-IS) in the context of Multiprotocol Label Switching (MPLS) Traffic Engineering (TE), in order to advertise some link characteristics such as the available bandwidth, traffic engineering metric, administrative group, and so on. By making statistical assumptions about the aggregated traffic carried onto a set of TE Label Switched Paths (LSPs) signalled with zero bandwidth (referred to as "unconstrained TE LSP" in this document), algorithms can be designed to load balance (existing or newly configured) unconstrained TE LSP across a set of equal cost paths. This requires knowledge of the number of unconstrained TE LSPs signalled across a link. This document specifies a new Link-type Traffic Engineering sub-TLV used to advertise the number of unconstrained TE LSPs signalled across a link. [STANDARDS-TRACK]

Extracted elements (15)

design-rationale §4

Care must be given to not trigger systematic flooding of IS-IS LSPs or OSPF LSAs at too high a granularity when the unconstrained TE LSP count changes, to avoid excessive control-plane churn.

mpls, routing

design-rationale §1

Unconstrained TE LSPs (signalled with zero bandwidth) follow IGP shortest paths and are used for fast-reroute protection meshes; in symmetric ECMP networks, path cost and hop count cannot serve as tie-breakers, motivating advertisement of LSP counts to enable load balancing algorithms.

mpls, routing

interoperability-note §3

The sub-TLV is carried within IS-IS extended IS reachability TLV (type 22) defined in RFC 5305 or the MT Intermediate Systems TLV (type 222) defined in RFC 5120, and within the OSPF TE Link TLV (Type 2) from RFC 3630 or OSPFv3 Intra-Area-TE LSA from RFC 5329.

mpls, routing

normative-requirement §3.1 MUST

If a second instance of the IS-IS Unconstrained TE LSP Count sub-TLV is present, the receiving system MUST only process the first instance.

mpls, routing

normative-requirement §3.2 MUST

If a second instance of the OSPF Unconstrained TE LSP Count sub-TLV is present, the receiving system MUST only process the first instance of the sub-TLV.

mpls, routing

normative-requirement §4 SHOULD

The absence of the Unconstrained TE LSP Count sub-TLV SHOULD be interpreted as an absence of information about the link, not as a zero count.

mpls, routing

normative-requirement §3.1 MUST NOT

The IS-IS Unconstrained TE LSP Count sub-TLV is OPTIONAL and MUST NOT appear more than once within the extended IS reachability TLV (type 22) or the MT Intermediate Systems TLV (type 222).

mpls, routing

normative-requirement §3.2 MUST NOT

The OSPF Unconstrained TE LSP Count sub-TLV is OPTIONAL and MUST NOT appear more than once within the Link TLV (Type 2) in the Traffic Engineering LSA or the OSPFv3 Intra-Area-TE LSA.

mpls, routing

normative-requirement §2 MAY

Unconstrained TE LSPs that are configured and provisioned through a management system MAY be omitted from the count that is reported.

mpls, routing

protocol-element §3.1

The IS-IS Unconstrained TE LSP Count sub-TLV has Type=23 (1 octet), Length=2 (1 octet), and a 2-octet Value field encoding the number of unconstrained TE LSPs signalled across the link.

mpls, routing

protocol-element §3.2

The OSPF Unconstrained TE LSP Count sub-TLV has Type=23 (2 octets), Length=4 (2 octets), and a 4-octet Value field encoding the number of unconstrained TE LSPs signalled across the link.

mpls, routing

registry §5

IANA assigned codepoint 23 to the Unconstrained TE LSP Count sub-TLV in the sub-registry for sub-TLVs carried in the OSPF TE Link TLV (type 2).

registry, mpls, routing

security-consideration §6

The Unconstrained TE LSP Count sub-TLV does not create any new security issues for OSPF or IS-IS; existing security frameworks from RFC 2328, RFC 5340, RFC 1195, and RFC 5304 apply.

security, mpls, routing

wire-format §3.1

IS-IS encoding: Type field is 1 octet (value 23), Length field is 1 octet (value 2), Value field is 2 octets carrying the unconstrained TE LSP count.

mpls, routing

wire-format §3.2

OSPF encoding: Type field is 2 octets (value 23), Length field is 2 octets (value 4), Value field is 4 octets carrying the unconstrained TE LSP count.

mpls, routing