EIGRP Topology

The show ip eigrp topology all-links command will display all possible paths to the destination. In addition to the successor and feasible successor routes, the topology table may also contain non-successor routes. A non-successor route is a route that does not satisfy the feasibility condition. The output shows the route to the network 192.168.0.0/24 now with three possible paths. The path via next hop 172.16.3.1 has a reported distance of 256000000, which is greater than the feasible distance for the route 409600. Since the feasibility condition is not satisfied, the path via 172.16.3.1 will not be a candidate for the successor role. When the router stays without routes that satisfy the FC, and a new path calculation for the prefix must be performed, the route will transit into the active state and the router will start querying neighbors for alternative routes.

EIGRP

Enhanced Interior Gateway Routing Protocol (EIGRP) is an advanced distance-vector routing protocol that is used on a computer network for automating routing decisions and configuration. The protocol was designed by Cisco Systems as a proprietary protocol, available only on Cisco routers. Partial functionality of EIGRP was converted to an open standard in 2013[1] and was published with informational status as RFC 7868 in 2016.

EIGRP is used on a router to share routes with other routers within the same autonomous system. Unlike other well known routing protocols, such as RIP, EIGRP only sends incremental updates, reducing the workload on the router and the amount of data that needs to be transmitted.

EIGRP replaced the Interior Gateway Routing Protocol (IGRP) in 1993. One of the major reasons for this was the change to classless IPv4 addresses in the Internet Protocol, which IGRP could not support.