Narbik’s Soup-to-Nuts Workbook EIGRP Lab 4

“Lab 4 - EIGRP Load Balancing” mostly covers the variance command. Variance command allows us to perform unequal cost load balancing if the feasibility condition is met. Only paths that are feasible can be used for load balancing and included in the routing table. The AD must be lower than the FD.

Advertised Distance (AD) is the distance to a particular destination as reported by a router to its neighbors. This distance is sometimes also called a Reported Distance and is equal to the current lowest total distance through a successor.

A Feasible Distance (FD) is the lowest known distance from a router to a particular destination since the last time the route went from Active to Passive state. It can be expressed in other words as a historically lowest known distance to a particular destination. While a route remains in Passive state, the FD is updated only if the actual distance to the destination decreases, otherwise it stays at its present value. On the other hand, if a router needs to enter Active state for that destination, the FD will be updated with a new value after the router transitions back from Active to Passive state. This is the only case when the FD can be increased. The transition from Active to Passive state in effect marks the start of a new history for that route.