Signalling Unnumbered Links in Resource ReSerVation Protocol - Traffic Engineering (RSVP-TE)
updated by
- rfc-6107 — Procedures for Dynamically Signaled Hierarchical Label Switched Paths
Extracted elements (20)
MPLS TE signalling did not support unnumbered links because the Explicit Route and Record Route Objects had no way to indicate an unnumbered link. This document extends RSVP-TE to fill that gap, while IGP TE extensions (IS-IS/OSPF) cover advertisement of unnumbered links separately.
The LSP_TUNNEL_INTERFACE_ID object class number is required to be of the form 11bbbbbb so that RSVP nodes that do not understand it will silently ignore but still forward it, preserving backward compatibility across the signalling path.
If an LSR originates an LSP advertised as an unnumbered Forwarding Adjacency, the LSR MUST allocate an identifier to that Forwarding Adjacency, and the Path message for that LSP MUST contain the LSP_TUNNEL_INTERFACE_ID object with the head end's Router ID and the allocated Interface ID.
If the ERO subobject used to determine the next hop is of type Unnumbered Interface ID and an RRO object was received (or is desired), an RRO subobject of type Unnumbered Interface ID MUST be appended to the RRO when sending the Path message downstream.
If the Path message contains the LSP_TUNNEL_INTERFACE_ID object, the tail-end LSR MUST allocate an identifier to the Forwarding Adjacency, and the Resv message MUST contain an LSP_TUNNEL_INTERFACE_ID object with the tail-end's Router ID and the tail-end's allocated Interface ID.
Router ID MUST be a stable IP address (typically a loopback) that remains reachable as long as the LSR has any connectivity, so that it does not become unusable when an interface goes down. It is RECOMMENDED to align with the OSPF 'Router Address' or IS-IS 'Traffic Engineering Router ID'.
When an LSR receives a Path message with an IF_ID RSVP_HOP IF_INDEX TLV that does not match any known <Router ID, local identifier> tuple, the LSR SHOULD return an error using the IF_ID ERROR_SPEC object with Error code 24 and Error value 16.
When processing an ERO with an Unnumbered Interface ID subobject, if the outgoing link is unnumbered, the Path message sent to the next hop MUST include the IF_ID RSVP_HOP object with the IP address set to the node's Router ID and Interface ID set to the identifier the node assigned to the link.
An Unnumbered Interface ID subobject belongs to an abstract node if that node's Router ID matches the subobject's Router ID field and the node has an unnumbered link or Forwarding Adjacency whose local identifier equals the subobject's Interface ID. ERO processing then follows RFC 3209 section 4.3.4.1.
An unnumbered link must be point-to-point. Each LSR at an end of the link assigns a non-zero 32-bit link identifier unique within that LSR's scope. The two endpoints exchange these identifiers (called local and remote identifiers from each side's perspective) via configuration, LMP, RSVP, or IGP extensions.
Processing an IF_ID RSVP_HOP IF_INDEX TLV requires the LSR to match the <IP Address, Interface ID> tuple in the TLV against its knowledge of neighbor-assigned identifiers as <Router ID, local identifier> to identify the link for label allocation.
The LSP_TUNNEL_INTERFACE_ID object may optionally appear in a Path message (called 'Forward Interface ID') or a Resv message (called 'Reverse Interface ID'). It is used to communicate the identifier allocated to a Forwarding Adjacency between head-end and tail-end LSRs.
The RRO Unnumbered Interface ID flag 0x01 (Local protection available) indicates the downstream link is protected via a local repair mechanism, and can only be set if the Local protection flag was set in the SESSION_ATTRIBUTE object of the Path message.
The RRO Unnumbered Interface ID flag 0x02 (Local protection in use) indicates a local repair mechanism is actively maintaining the tunnel, typically after an outage of the originally routed link.
IANA must assign a class number of the form 11bbbbbb to the LSP_TUNNEL_INTERFACE_ID object (class 193), which causes RSVP to silently ignore and forward the object if unrecognized.
IANA must assign a new subobject type number (Type 4, Unnumbered Interface ID) for both the EXPLICIT_ROUTE object and the ROUTE_RECORD object, following the assignment rules of RFC 3209 and BCP 26 (RFC 2434).
This document makes a small extension to RFC 3209 to support unnumbered links and poses no new security concerns. The authors note that the additional interface identifier could make an RSVP message harder to spoof.
The LSP_TUNNEL_INTERFACE_ID object has class number 193, C-Type 1, and length 12. It contains a 32-bit LSR Router ID field followed by a 32-bit Interface ID field.
The Unnumbered Interface ID subobject for the ERO has Type 4, Length 12, and contains a Reserved 16-bit field (MUST be zero), a 32-bit Router ID, and a 32-bit Interface ID identifying the unnumbered link local to the specified router.
The Unnumbered Interface ID subobject for the RRO has Type 4, Length 12, and contains an 8-bit Flags field, a Reserved byte (MBZ), a 32-bit Router ID, and a 32-bit Interface ID. Defined flags are 0x01 (Local protection available) and 0x02 (Local protection in use).