ECMP, MPLS Load Balancing

http://packetpushers.net/fat-or-entropy-label/

The hashing in the MPLS Core vary from vendors, let’s take the example of Cisco, for IP payloads the load-balancing is done on IP header (L3/L4 fields) and for non-IP payloads it is done on the last label, this is required to preserve the characteristics of the emulated service (VPWS).
The routers distinguish the IP from non-IP payloads by checking the version field of the paylods: 4 for IPv4 and 6 for IPv6. But unfortunately if you have some non-IP payloads that starts with 4 or 6, the load-balancing can be messy, and it already happens with MAC addresses starting with 4 ;). So Cisco highly recommend to use for non-IP payloads in the L2VPN the CW which starts with a 0.

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