Equal-Cost Paths and Load Sharing Overview
For equal-cost paths, load sharing is based on the BGP next hop. For example, if four prefixes all point to a next hop and there is more than one equal-cost path to that next hop, the routing protocol process uses a hash algorithm to choose the path among the four prefixes. Also, for each prefix, the routing protocol process installs a single forwarding entry pointing along one of the paths. The routing software does not rehash the path taken as prefixes pointing to the next hop come and go, but it does rehash if the number of paths to the next hop changes. Because a prefix is tied to a particular path, packet reordering should not happen. The degree of load sharing improves as the number of prefixes increases.