Application of LFA Policy to Adjacency SID Tunnel

The modifications to TI-LFA and RLFA as described in Application of LFA Policy to a Segment Routing Node SID Tunnel are also applied to adjacency SID tunnel in a similar fashion.

The LFA selection algorithm for an adjacency to a neighbor is modified by applying the LFA policy of the link of the protected adjacency. It adheres to the following preference order:

  1. Adjacency of an alternate parallel link to the same neighbor, determined as follows:

    1. apply admin-group and SRLG constraints of the LFA policy of the link of the protected adjacency

    2. select the adjacency with best admin-group(s) according to the preference specified in the value of the include-group option in the route next-hop policy template

    3. select the adjacency with lowest metric

    4. select the adjacency to the neighbor with the lowest router ID (OSPF) or system ID (IS-IS), and the lowest metric

    5. select the adjacency over the lowest interface index, and the lowest neighbor router ID (OSPF) or system ID (IS-IS)

  2. ECMP next hop to a node-SID of the same neighbor, determined as follows:

    1. apply admin-group and SRLG constraints of the LFA policy of the link of the protected adjacency

    2. select the next hop with the best admin-group(s) according to the preference specified in the value of the include-group option in the route next-hop policy template

    3. select the next hop with lowest metric

    4. select the next hop to the neighbor with the lowest router ID (OSPF) or system ID (ISIS), and the lowest metric

    5. select the next hop over the lowest interface index, and the lowest neighbor router ID (OSPF) or system ID (IS-IS)

  3. LFA backup outcome of a of a node SID of the same neighbor

    1. select a LFA backup with an outgoing link that does not conflict with the LFA policy of the link of the protected adjacency

      Note: If a different LFA policy was already applied in the computation of the LFA backup of the node SID of the neighbor, it is possible that some links to that node SID may have been eliminated before applying the LFA policy of the link of the protected adjacency.
Parent topic: LFA Policies