BGP - Equal Cost Multipath AS_Path Attribute

When applying equal cost multipath in a BGP topology, there are certain prerequisites that must be fulfilled in order for candidate routes to be considered for multipath. Certain BGP attributes must be the same in order for a second path to be considered for equal cost multipath.

One of those attributes is the AS_Path. By default, both the sequence of ASNs as well as the actual AS Path Length are examined and must be the same. However, this requirement can be relaxed using the following BGP router mode command:

R1(config-router)#bgp bestpath as-path multipath-relax

This command tells BGP to “relax” its requirement of having the same AS path numbers AND AS path length to only checking the AS path length.


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