RSVP-TE Summary Fast Reroute Extensions for Label Switched Path (LSP) Tunnels
updates
- rfc-4090 — Fast Reroute Extensions to RSVP-TE for LSP Tunnels
Extracted elements (25)
A race condition can arise when the MP triggers a refresh without a B-SFRR-Ready object while the PLR simultaneously triggers Summary FRR due to a concurrent fault. The MP will receive an Srefresh with an unknown Message_Identifier, generate an Srefresh NACK per RFC 2961, and the PLR recovers by replaying the full Path state. No special new mechanism is required.
Per-LSP FRR signaling in RFC 4090 causes control-plane scalability and latency issues on PLR and MP nodes when a failure affects tens of thousands of LSPs traversing the same link. Summary FRR addresses this by allowing signaling to be performed on one or more per-bypass tunnel groups rather than individually for each protected LSP.
The PLR assigns protected LSPs sharing the same outgoing protected interface, the same bypass tunnel, and the same tunnel sender address to the same Bypass_Group_Identifier. This minimizes the number of bypass tunnel Summary FRR groups and optimizes signaling volume between PLR and MP after FRR.
The Extended ASSOCIATION object is defined in RFC 4872 with class number in the form 11bbbbbb, ensuring that nodes not supporting these extensions will ignore the object and forward it unmodified, in accordance with RFC 2205 Section 3.10 unknown-class object handling. The extensions are thus fully backwards compatible.
A failure during merge processing of any individual rerouted LSP MUST result in an RSVP PathErr message. After successful merge, the MP node SHOULD immediately use summary refresh procedures to refresh the protected LSP Resv state rather than sending individual RSVP Resv messages.
A PLR node considers a protected LSP as Summary FRR capable only if all fields in the B-SFRR-Ready Extended Association ID sent in the RSVP Path message match those received in the RSVP Resv message (except MESSAGE_ID). If fields do not match or the object is absent in a subsequent refresh, the PLR MUST consider the LSP as not Summary FRR capable.
A PLR node MUST generate a new Message_Identifier each time the contents of the B-SFRR-Ready Extended Association ID change, such as when the PLR node changes the bypass tunnel assignment.
Before Summary FRR procedures can be used, a handshake MUST be completed between the PLR and MP nodes using the B-SFRR-Ready Extended ASSOCIATION object exchanged in both RSVP Path and Resv messages of the protected LSP.
For Summary FRR-capable LSPs assigned to the same bypass tunnel, a common RSVP_HOP and SENDER_TEMPLATE MUST be used post-failure. The PLR MUST signal non-Summary FRR-capable LSPs over the bypass tunnel before signaling the Summary FRR-capable LSPs.
The Association Source, Association Type, and Association ID in the B-SFRR-Ready Extended ASSOCIATION object MUST be set as defined in RFC 4872. The Association Source is set to an address of the PLR node, and the Global Association Source MUST be set per RFC 6780.
The PLR node MUST ensure that the bypass tunnel assignment can satisfy the protected LSP MTU requirements post-FRR, preventing packets from being dropped due to exceeding the MTU size of the backup path after traffic is rerouted.
The PLR node MUST generate a MESSAGE_ID object with Epoch and Message_Identifier set according to RFC 2961. The MESSAGE_ID object Flags MUST be cleared when transmitted by the PLR node and ignored when received at the MP node.
The received B-SFRR-Ready Extended Association ID contents in the RSVP Resv message MUST match the latest B-SFRR-Ready Extended ASSOCIATION object and Association ID contents that the PLR had sent in the RSVP Path message (except MESSAGE_ID) to constitute a valid acknowledgment.
When forwarding an RSVP Resv message upstream, the PLR node SHOULD remove any B-SFRR-Ready Extended ASSOCIATION objects whose Bypass_Source_IPv4_Address or Bypass_Source_IPv6_Address matches any PLR node address. Similarly, the MP SHOULD remove objects whose Bypass_Destination address matches any MP node address when forwarding Path messages downstream.
The B-SFRR-Active Extended ASSOCIATION object is sent by the PLR node within the RSVP Path message of the bypass tunnel after a failure, informing the MP that one or more groups of protected LSPs (identified by Bypass_Group_Identifiers) are being rerouted over the bypass tunnel. It carries a shared RSVP_HOP object, TIME_VALUES, and tunnel sender address applicable to all identified groups.
The B-SFRR-Ready Extended ASSOCIATION object is added by the PLR in the RSVP Path message of each protected LSP to record the bypass tunnel assignment, including the Bypass_Group_Identifier and a MESSAGE_ID. The MP acknowledges by echoing the object in the RSVP Resv message, completing the pre-failure handshake required before Summary FRR can be activated.
The Bypass_Group_Identifier is a 32-bit value created and managed by the PLR node that groups protected LSPs sharing the same bypass tunnel, egress link, and tunnel sender address. It is exchanged via B-SFRR-Ready signaling so the MP can build a mirrored Summary FRR group database.
IANA updated the 'Association Type' subregistry under 'Generalized Multi-Protocol Label Switching (GMPLS) Signaling Parameters' to add two new values: value 5 for 'B-SFRR-Ready Association' (Bypass Summary FRR Ready) and value 6 for 'B-SFRR-Active Association' (Bypass Summary FRR Active).
Existing mechanisms for maintaining the integrity and authenticity of RSVP messages per RFC 2747 (RSVP Cryptographic Authentication) can be applied to protect against message interception and tampering. Security considerations from RFC 4090 and RFC 5920 (MPLS/GMPLS Security Framework) also apply.
Interception of signaling messages carrying the new Extended ASSOCIATION objects discloses slightly more network state information than RFC 4090 alone. More critically, a single rogue RSVP message can manipulate the entire group of protected LSPs assigned to the same bypass tunnel group, though such an attack is possible without these extensions at a higher per-LSP signaling cost.
A protected LSP progresses through states: (1) unprotected — no B-SFRR-Ready object; (2) Summary FRR capable — PLR has sent B-SFRR-Ready in Path and received matching acknowledgment in Resv; (3) Summary FRR active — failure occurred, PLR sent B-SFRR-Active in bypass tunnel Path; (4) merged — MP applied B-SFRR-Active and resumed Srefresh. An LSP cannot join a group already in FRR active state.
The IPv4 B-SFRR-Active Extended Association ID contains: Num-BGIDs (16 bits), Reserved (16 bits), one or more Bypass_Group_Identifier fields (32 bits each), an RSVP_HOP_Object (Class 3, C-Type 1 for IPv4), TIME_VALUES object (Class 5), and IPv4 tunnel sender address (32 bits).
The IPv4 B-SFRR-Ready Extended Association ID contains: Bypass_Tunnel_ID (16 bits), Reserved (16 bits), Bypass_Source_IPv4_Address (32 bits), Bypass_Destination_IPv4_Address (32 bits), Bypass_Group_Identifier (32 bits), and MESSAGE_ID object as defined by RFC 2961.
The IPv6 B-SFRR-Active Extended Association ID contains: Num-BGIDs (16 bits), Reserved (16 bits), one or more Bypass_Group_Identifier fields (32 bits each), RSVP_HOP_Object (Class 3, C-Type 2 for IPv6), TIME_VALUES object (Class 5), and IPv6 tunnel sender address (128 bits).
The IPv6 B-SFRR-Ready Extended Association ID contains: Bypass_Tunnel_ID (16 bits), Reserved (16 bits), Bypass_Source_IPv6_Address (128 bits), Bypass_Destination_IPv6_Address (128 bits), Bypass_Group_Identifier (32 bits), and MESSAGE_ID object.