Uniform Failover From Primary To Backup Ilm - Alcatel-Lucent 7450 Manual

If one or more ECMP next-hops for the root LSR prefix exist, LDP picks the interface for the
primary ILM based on the rules of mLDP FEC resolution specified in RFC 6388:
1. The candidate upstream LSRs are numbered from lower to higher IP address.
2. The following hash is performed: H = (CRC32(Opaque Value)) modulo N, where N is the
3. The selected upstream LSR U is the LSR that has the number H.
LDP then picks the interface for the backup ILM using the following new rules:
1. if (H + 1 < NUM_ECMP) {
In some topologies, it is possible that none of ECMP or LFA next-hop will be found. In this case,
LDP programs the primary ILM only.

Uniform Failover from Primary to Backup ILM

When LDP programs the primary ILM record in the data path, it provides the IOM with the
Protect-Group Identifier (PG-ID) associated with this ILM and which identifies which upstream
LSR is protected.
In order for the system to perform a fast switchover to the backup ILM in the fast path, LDP
applies to the primary ILM uniform FRR failover procedures similar in concept to the ones
7450 ESS MPLS Guide
number of upstream LSRs. The Opaque Value is the field identified in the P2MP FEC
Element right after 'Opaque Length' field. The 'Opaque Length' indicates the size of the
opaque value used in this calculation.
// If the hashed entry is not last in the next-hops then pick up the next as backup.
backup = H + 1;
} else {
// Wrap around and pickup the first.
backup = 1;
}
Label Distribution Protocol
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