What happens if a routing table has two or more paths with identical metrics to the same destination network?
When a router has two or more paths to a destination with equal cost metrics, then the router forwards the packets using both paths equally. This is called equal cost load balancing. The routing table contains the single destination network, but has multiple exit interfaces, one for each equal cost path. The router forwards packets using the multiple exit interfaces listed in the routing table.
If configured correctly, load balancing can increase the effectiveness and performance of the network. Equal cost load balancing can be configured to use both dynamic routing protocols and static routes.
Note: Only EIGRP supports unequal cost load balancing.
The animation in the figure provides an example of equal cost load balancing.