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 ECMP, alcatel-lucent service routers, SR 7750

Traffic Flow Without ECMP
Think 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

One Response to “ECMP (Equal Cost Multi Path)”

  • Thanks bro. really appreciate this.

    Much to learn am Just a CCNP trying to get the experience to move up

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