CISCO IOS in a Nutshell

EIGRP

EIGRP stands for Enhanced IGRP. EIGRP, like IGRP, is a proprietary Cisco protocol; other vendors’ routers cannot support EIGRP, but that’s about the only disadvantage. EIGRP provides excellent performance, easy configuration, VLSM support, and support for IPX and AppleTalk. It is a distance-vector protocol that also contains the characteristics of a link-state protocol. EIGRP uses the same compound metric as its predecessor, IGRP. And unlike IGRP, which is prone to routing loops, EIGRP is pretty much loop-free. The most unique feature of EIGRP is its dual finite state machine, which provides an extremely fast convergence time. Other features are partial routing table updates (less bandwidth and CPU are used on routing updates), automatic discovery of neighbors, and increased scalability.

Enabling EIGRP on the Network

Here are the EIGRP configurations for Router 1, Router 2, and Router 3 in Figure 9-1. By now, these configurations should look familiar—they’re almost identical to the IGRP configurations, except for the name of the protocol.

The configuration for Router 1 is:

interface Ethernet0
 ip address 172.16.1.1 255.255.255.0
!
interface Serial0
 bandwidth 125
 ip address 192.168.3.1 255.255.255.0
!
interface Serial1
 bandwidth 125
 ip address 192.168.1.1 255.255.255.0
!
router eigrp 101
  network 172.16.0.0
  network 192.168.1.0
  network 192.168.3.0

For Router 2, the configuration is:

interface Ethernet0 ip address 172.17.1.1 255.255.255.0 ! interface Serial0 bandwidth 125 ip address ...