A feasible successor is the Enhanced Interior Gateway Routing Protocol (EIGRP) neighbor that has a reported distance that is lower than the feasible distance of the current best path. A feasible successor must have a valid, loop-free path to the destination. If these conditions are met, EIGRP immediately installs the feasible successor in the Routing Information Base (RIB) in order to speed up convergence should the best path become unavailable.

Feasible distance is the EIGRP term for the best metric along a path to a destination. The feasible distance includes the metric to the EIGRP neighbor that is advertising the path.
Reported distance, not feasible distance, is the total metric along a path to a destination. The reported distance is determined by using the metric of the path as advertised by an upstream EIGRP neighbor. The reported distance might also be the highest metric or the lowest metric along a path to a destination.