Advertising Redundancy Policy in BGP

Redundancy protection is a generalized protection mechanism by replicating and transmitting copies of flow packets on redundancy node over multiple different and disjoint paths, and further eliminating the redundant packets at merging node. To support the replication on the redundancy node, Redundancy Segment and Redundancy Policy are specified respectively. Redundancy Segment is the variation of Binding SID to associate with a Redundancy Policy, instantiation of which provides segment lists of more than one disjoint paths. Redundancy Policy is a variant of SR Policy , and shares the basic structure and elements with SR Policy. Different from SR policy, a new attribute Flag is added to indicate the type of the Candidate Path as redundancy type, which means all the Segment-Lists in this candidate path are used to forward the different copies of service traffics. This document defines the extensions to Border Gateway Protocol (BGP) to distribute the redundancy policy information. As a variant of SR policy, Redundancy Policy reuses the BGP extensions to SR policy candidate path and other information distribution specified in . In addition, a new sub-TLV is defined in this document to support the distribution of new attribute of redundancy policy.

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.

As a variant of SR policy, redundancy policy uses the same Subsequent Address Family Identifier (SAFI) whose NLRI identifies an SR Policy candidate path. The Tunnel Type identifier for SR Policy and a set of sub-TLVs specifying segment lists of the SR Policy candidate path, as well as other information about the SR Policy are reused. The content of Redundancy Policy Candidate Path is encoded in the Tunnel Encapsulation Attribute by using the same Tunnel-Type of SR Policy Type. The redundancy policy encoding structure is as follows:

Attributes: Tunnel Encaps Attribute (23) Tunnel Type: SR Policy Binding SID SRv6 Binding SID Redundancy Flag Preference Priority Policy Name Policy Candidate Path Name Explicit NULL Label Policy (ENLP) Segment List Segment Segment ... ... ]]>

Redundancy policy introduces a new attribute Flag to indicate the type of Candidate Path as redundancy type. Correspondingly, a new Flag sub-TLV is defined to be attached at the candidate path level as a sub-TLV. The Flag sub-TLV is optional and MUST NOT appear more than once in the Redundancy Policy encoding.

Candidate Path Flag Sub-TLV where: Type: to be allocated by IANA. Length: specifies the length of the value field not including Type and Length fields. Flags: 1 octet of flags. It is requested to IANA to create a new registry "SR Policy Candidate Path Flags" . One flag is defined at this writing:

Candidate Path Flags R-Flag: This flag encodes the redundancy policy behavior U-Flag: Unused and unassigned RESERVED: 1 octet of reserved bits. SHOULD be set to zero on transmission and MUST be ignored on receipt.

Redundancy Policy can be optionally associated with a Binding Segment, which can only be Redundancy Segment. When there is a Redundancy Segment associated with Redundancy Policy, Redundancy Segment is required to be distributed by the Binding SID Sub-TLV or SRv6 Binding SID Sub-TLV defined in section 2.4.2 and 2.4.3 of respectively. In SRv6, the endpoint behavior End.R of Redundancy Segment is required to be distributed with SRv6 Binding SID at the same time.

This document defines new sub-TLVs in the registry "BGP Tunnel Encapsulation Attribute sub-TLVs" that has been assigned codepoints by IANA as follows via the early allocation process:

TBD