Load Balancing

You may be wondering what happens if a routing table has two or more paths with the same metric to the same destination network. When a router has multiple paths to a destination network and the value of that metric (hop count, bandwidth, etc.) is the same, this is known as an equal cost metric, and the router will perform equal cost load balancing. The routing table will contain the single destination network but will have multiple exit interfaces, one for each equal cost path. The router will forward packets using the multiple exit interfaces listed in the routing table.
Just in case you are wondering, a router can send packets over multiple networks even when the metric is not the same if it is using a routing protocol that has this capability. This is known as unequal cost load balancing. EIGRP (as well as IGRP) are the only routing protocols that can be configured for unequal cost load balancing. Unequal cost load balancing in EIGRP is not discussed in this course but is covered in CCNP.


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