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MPLS and dual equal-cost paths

jkeeffe
Level 2
Level 2

If a site has two outbound WAN routers (for redundancy) that are configured as PE routers with the WAN interfaces configured with MPLS, will two LSPs be created using LDP (one from each PE) allowing the WAN routers to loadbalance traffic across the MPLS backbone?

1 Reply 1

Akash Agrawal
Cisco Employee
Cisco Employee

Load balancing is very much possible in MPLS environment. Following are the general rules for load balancing labeled packets

1. If the MPLS payload is an IPV4 packet, the load balancing is done by hashing the source and destination IP address of the IPv4 header

2.IF the MPLS payload is an IPv6 packet, the load balancing is done by hashing the source and destination IP address of the IPv6 header.

3.If the MPLS payload is not an IPv4 packet, the load balancing is done by looking at the value of the bottom label

Label stack does not have protocol identifier field so to know what is the MPLS payload is, router can look first nibble following the MPLS label stack, if it is 4 then router considers this an IPv4 packet and performs IPv4 CEF hashing. if it is

6 , MPLS payload is considered IPv6, and the router performs IPv6 CEF hashing

For more information you can refer book "MPLS fundamentals" by Luc De Ghein.