Enhanced Interior Gateway Routing Protocol (EIGRP) is an advanced distance vector routing protocol developed by Cisco Systems. As the name suggests, EIGRP is an enhancement of another Cisco routing protocol IGRP (Interior Gateway Routing Protocol). IGRP is an older classful, distance vector routing protocol, now obsolete since IOS 12.3.

EIGRP is a distance vector routing protocol that includes features found in link-state routing protocols. EIGRP is suited for many different topologies and media. In a well-designed network, EIGRP can scale to include multiple topologies and can provide extremely quick convergence times with minimal network traffic.

This chapter introduces EIGRP and provides basic configuration commands to enable it on a Cisco IOS router. It also explores the operation of the routing protocol and provides more detail on how EIGRP determines best path.