ECMP (Equal Cost Multi Path)

If the total IGP cost to a destination are same for two path, these paths are called Equal Cost Multi Path. Normally if there are two path that have same IGP cost, in Alcatel-Lucent Service Routers, lower interface wins and the traffic goes through it.

 

Traffic Flow Without ECMPThink about the above topology, without ECMP the traffic only goes through the A path. And when you use the below commands to see the tables, you will realize the below results:

show router ldp bindings (2 path, A and B)

show router fib 1 (1 path, A)

For more information about LDP, T-LDP and CR-LDP, check the related following RFCs…
RFC 5036: LDP Specification
RFC 3815: Definitions of Managed Objects for the MPLS,LDP
RFC 3478: Graceful Restart Mechanism for Label Distribution Protocol
RFC 5443: LDP IGP Synchronization
RFC 7307: LDP Extensions for Multi-Topology
RFC 7361: LDP Extensions for Optimized MAC Address Withdrawal in a H-VPLS
RFC 3212: Constraint-Based LSP Setup using LDP
RFC 3213: Applicability Statement for CR-LDP
RFC 3214: LSP Modification Using CR-LDP