Overview
EIGRP is a Cisco proprietary routing protocol. EIGRP supports IP using both classless and class-based IP addresses, as well as other network-layer protocols. This allows networks using classless interdomain routing (CIDR)-compliant IP addresses or variable-length subnet mask (VLSM) to use Cisco distance-vector routing technology. Other enhancements were designed to reduce convergence times and improve network stability. One such enhancement was a new algorithm, the Diffusing Update Algorithm (DUAL), which enables EIGRP routers to determine whether a path advertised by a neighbor is looped or loop free, and allows a router running EIGRP to find alternative paths without waiting for updates from other routers. This helps EIGRP networks converge quickly, without incurring any significant risk of introducing or propagating routing loops.

This chapter examines the architectural framework of EIGRP, its operational mechanics, and the similarities and differences between EIGRP and IGRP. It also focuses on EIGRP features and operation, as well as the steps required to configure and test EIGRP networks. Understanding how EIGRP functions will help you determine whether it is the appropriate routing protocol for your environment.