Multipath Issues in Unicast and Multicast Next-Hop Selection

Various routing protocols, including Open Shortest Path First (OSPF) and Intermediate System to Intermediate System (ISIS), explicitly allow “Equal-Cost Multipath” (ECMP) routing.  Some router implementations also allow equal-cost multipath usage with RIP and other routing protocols.  The effect of multipath routing on a forwarder is that the forwarder potentially has several next-hops for any given destination and must use some method to choose which next- hop should be used for a given data packet.