IP Routing

Chapter 4. Enhanced Interior Gateway Routing Protocol (EIGRP)

The Enhanced Interior Gateway Routing Protocol (EIGRP), referred to as an advanced Distance Vector protocol, offers radical improvements over IGRP. Traditional DV protocols such as RIP and IGRP exchange periodic routing updates with all their neighbors, saving the best distance (or metric) and the vector (or next hop) for each destination. EIGRP differs in that it saves not only the best (least-cost) route but all routes, allowing convergence to be much quicker. Further, EIGRP updates are sent only upon a network topology change; updates are not periodic.

Getting EIGRP running is not much more difficult than getting IGRP running, as we will see in Section 4.1.

Even though EIGRP offers radical improvements over IGRP, there are similarities between the protocols. Like IGRP, EIGRP bases its metric on bandwidth, delay, reliability, load, and MTU (see Section 4.2).

The fast convergence feature in EIGRP is due to the Diffusing Update Algorithm (DUAL), discussed in Section 4.3.

EIGRP updates carry subnet mask information. This allows EIGRP to summarize routes on arbitrary bit boundaries, support classless route lookups, and allow the support of Variable Length Subnet Masks (VLSM). This is discussed in Section 4.4 and Section 4.5.

Setting up default routes in EIGRP is discussed in Section 4.6.

Troubleshooting EIGRP can be tricky. This chapter ends with some troubleshooting tips in Section 4.7.

EIGRP is a Cisco proprietary protocol; ...