EIGRP Successor and Feasible Successor

An Eigrp Successor is a neighboring router that has a least-cost path to a destination (lowest FD) that is guaranteed not to be part of a routing loop. Successors are offered to the routing table to be used for forwarding packets

Feasible Successor is the Next-Hop router for the backup path. To qualify as a feasible successor, a Next-Hop router must have an AD (Administrative Distance) less than the FD of the Current Successor Route. Feasible Successors are kept in Topology Table. Topology Table can maintain multiple FS for a Destination.

“Feasible Distance (FD )is the accumulated cost between the local router to the Next-Hop Router and the Next-Hop Router to the Destination. The Cost between the Next-Hop Router and the Destination is known as Advertised Distance, and the Sum of Advertised Distance and the Cost between Local Router and Next-Hop Router is known as Feasible Distance.”