IGP Routing Protocol Extensions for Discovery of Traffic Engineering Node Capabilities
Extracted elements (21)
A single capability bit registry is defined for both OSPF and IS-IS rather than separate per-protocol registries, under a new IGP-TE base registry, to avoid divergence between the two protocols and simplify management of shared TE node capability semantics.
Advertising control plane TE node capabilities (such as GMPLS or P2MP signaling support) allows path computation to select routes avoiding nodes that do not support a given feature, or to trigger fallback mechanisms (e.g., LSP hierarchy for legacy transit LSRs), facilitating backward compatibility.
The flooding scope of the TE Node Capability Descriptor is deliberately area-local rather than domain-wide because the capabilities are used as constraints during path selection, and domain-wide flooding would be unnecessary for intra-area TE path computation and would increase overhead.
For OSPF, a router not supporting the TE Node Capability Descriptor TLV will silently ignore it as specified in RFC 4970. For IS-IS, a router not supporting the sub-TLV will silently ignore it as specified in RFC 4971. Absence of the TLV means TE capabilities of that LSR are unknown.
A capability change MAY trigger Constrained Shortest Path First (CSPF) computation but MUST NOT trigger normal SPF computation, since the TE Node Capability TLV is not used for SPF or normal routing.
A router MUST originate a new OSPF Router Information LSA whenever the content of the TE Node Capability Descriptor TLV changes or whenever required by regular OSPF procedure (LSA refresh every LSRefreshTime).
An IS-IS router MUST originate a new IS-IS LSP whenever the content of any TE Node Capability sub-TLV changes or whenever required by regular IS-IS procedure (LSP refresh).
For IS-IS, the TE Node Capability Descriptor sub-TLV MUST be carried within an IS-IS CAPABILITY TLV having the S flag cleared, limiting flooding to area-local scope.
Reserved bits in the IS-IS TE Node Capability Descriptor sub-TLV MUST be set to zero on transmission and MUST be ignored on reception. Any unknown bit flags SHALL be treated as reserved.
Reserved bits in the OSPF TE Node Capability Descriptor TLV MUST be set to zero on transmission and MUST be ignored on reception. Any unknown bit flags SHALL be treated as reserved.
The TE Node Capability Descriptor sub-TLV is OPTIONAL and MUST NOT appear more than once in an IS-IS Router Capability TLV.
The TE Node Capability Descriptor TLV is OPTIONAL and MUST NOT appear more than once in an OSPF Router Information LSA. If it appears more than once, only the first occurrence MUST be processed and others MUST be ignored.
The TE Node Capability Descriptor TLV MUST be carried within an OSPFv2 type 10 Router Information LSA or an OSPFv3 Router Information LSA with the S1 bit set and the S2 bit cleared, limiting flooding scope to area-local.
Five TE Node Capabilities are defined: B bit (P2MP branch node), E bit (P2MP bud-LSR, both transit and egress), M bit (MPLS-TE signaling support), G bit (GMPLS signaling support), and P bit (P2MP MPLS-TE signaling support).
The TE Node Capability Descriptor contains a variable-length set of bit flags where each bit corresponds to a given TE node capability, describing both data plane and control plane capabilities of an LSR for use during path computation.
IANA assigned codepoint 1 from the IS-IS CAPABILITY TLV sub-TLV registry (defined in RFC 4971) for the IS-IS TE Node Capability Descriptor sub-TLV.
IANA assigned codepoint 5 from the Router Information LSA TLV registry (defined in RFC 4970) for the OSPF TE Node Capability Descriptor TLV.
IANA created a new capability bit flags registry (sub-registry under a new IGP-TE base registry covering both OSPF and IS-IS) with five initial assignments: bit 0 (B, P2MP Branch LSR), bit 1 (E, P2MP Bud LSR), bit 2 (M, MPLS-TE), bit 3 (G, GMPLS), bit 4 (P, P2MP RSVP-TE). New bit allocations require IETF Consensus.
Tampering with the TE Node Capability Descriptor TLV may affect Traffic Engineering computation, but since it is not used for SPF computation or normal routing, it has no direct effect on IP routing. Existing IS-IS Link State PDU security mechanisms (RFC 3567) and OSPF LSA security (RFC 2154) can be used to secure this TLV.
The IS-IS TE Node Capability Descriptor sub-TLV uses type 1, variable length, with a value field consisting of an array of 8-bit units of flags numbered from the most significant bit as bit zero. Format follows RFC 3784: 1-octet type, 1-octet length, value field.
The OSPF TE Node Capability Descriptor TLV uses type 5, variable length (multiple of 4), with a value field consisting of an array of 32-bit words of flags numbered from the most significant bit as bit zero. Format follows RFC 3630: 2-octet type, 2-octet length, value field.