Equal Cost Load Balancing
EIGRP permits multiple successor routes with an equal metric to be installed into the routing table for load balancing.
Installing multiple routes for the same prefix is known as equal cost multipathing, or ECMP.
Unequal Cost Load Balancing
EIGRP also supports unequal-cost load balancing, which permits the installation of the successor routes and feasible successors into the routing table.
This is accomplished by changing the variance multiplier on the routers configuration.
The variance value calculated is the successors feasible distance for a route multiplied by the variance multiplier value. Any feasible successors feasible distance metric that is lower than the variance value is eligible to be inserted into the routing table. EIGRP will install routes up to the number of maximum paths permitted in the routers configuration.