Nokia 7705 SAR-W Series Manual page 409

MPLS Guide
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, Label Distribution Protocol Extensions for Point-to-Multipoint and Multipoint-to-
Multipoint Label Switched Paths:
LDP then picks the interface for the backup ILM using the following new rules:
In some topologies, it is possible that no ECMP or LFA next hop is found. In this case,
LDP programs the primary ILM only.
3HE 18686 AAAB TQZZA
1. The candidate upstream LSRs are numbered from lowest to highest IP address.
2. The following hash is performed:
H = (CRC32(Opaque Value)) modulo N
where N is the number of upstream LSRs
The Opaque Value is the field in the point-to-multipoint FEC element
immediately after the Opaque Length field. The Opaque Length indicates the
opaque value used in this calculation.
3. The selected upstream LSR U is the LSR that has the number H.
if (H + 1 < NUM_ECMP) {
// 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 pick up the first.
backup = 1;
}
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Label Distribution Protocol
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