Final answer:
The 'variance' command is used in EIGRP for unequal-cost load balancing, allowing multiple paths to be used if their metrics are within a specified multiple of the best path's metric.
Step-by-step explanation:
The variance command is used to determine whether EIGRP feasible successors can be used for unequal-cost load balancing. Enhanced Interior Gateway Routing Protocol (EIGRP) allows for a routing protocol mechanism called variance to implement unequal-cost load balancing. With the variance command, EIGRP can use multiple paths to destinations if the paths' metrics are within a specified variance of the best path's metric.
For example, if the best route has a metric of 10, and the variance is set to 2, any routes with a metric less than or equal to 20 (10 * 2) could be used as feasible successors and participate in load balancing. This mechanism is crucial for network engineers who aim to optimize their network performance and maximize the use of all possible routes.