OSPF equal-cost multipath (ECMP) for different subnets available through the same next-hop routes

The switches support optional load-sharing across redundant links where the network offers two, three, or four equal-cost next-hop routes for traffic to different subnets. (All traffic for different hosts in the same subnet goes through the same next-hop router.)

For example, in the OSPF network shown in the following figure, IP load-sharing is enabled on router "A". In this case, OSPF calculates three equal-cost next-hop routes for each of the subnets and then distributes per-subnet route assignments across these three routes.

Example of load-sharing traffic to different subnets through equal-cost next-hop routers

Example of a routing table for the network in the preceding figure:

IP load-sharing does not affect routed traffic to different hosts on the same subnet. That is, all traffic for different hosts on the same subnet will go through the same next-hop router. For example, if subnet 10.32.0.0 includes two servers at 10.32.0.11 and 10.32.0.22, all traffic from router "A" to these servers will go through router "B".