Prefix SID resolution for segment routing mapping server

The following processing rules apply for prefix SID resolution.

• For a specific prefix, IGP selects the SID value among multiple advertised values in the following order:

  1. local intra-area SID owned by this router

  2. prefix SID sub-TLV advertised within a OSPF Extended Prefix TLV

     If multiple SIDs exist, select the SID corresponding to the destination router or ABR with the lowest OSPF Router ID which is reachable via the first next hop of the prefix

  3. OSPF Extended Prefix Range TLV from mapping server

     If multiple SIDs exist, select the following, using the preference rules in draft-ietf-spring-conflict-resolution-05 when applied to the SRMS entries of the conflicting SIDs. The order of these rules is as follows:

     1. smallest range
     2. smallest starting address
     3. smallest algorithm
     4. smallest starting SID

• The selected SID is used with all ECMP next hops from step 1 toward all destination nodes or ABR nodes which advertised the prefix.

• If duplicate prefix SIDs exist for different prefixes after above steps, the first SID which is processed is programmed for its corresponding prefix. Subsequent SIDs causes a duplicate SID trap message and are not programmed. The corresponding prefixes are still resolved normally using IP next hops.