Core Issue:
Enhanced Interior Gateway Routing Protocol (EIGRP) is a Cisco proprietary enhanced distance vector routing protocol. It relies on the Diffusing Update Algorithm (DUAL) to calculate the shortest path to a destination. It is similar to its predecessor, Interior Gateway Routing Protocol (IGRP), in calculating the metric. However, it has many improvements, such as fast convergence, incremental updates and support for multiple network layer protocols. EIGRP acts as a distance vector protocol for calculating the best path to a destination, but it behaves like a link state protocol to propagate routing information and adapt to topology changes.
Resolution:
To configure EIGRP for IP, issue the router eigrp as-number command in global configuration mode. The as-number has to be the same on different routers to accept routing information from each other.
To enable EIGRP on the desired interfaces that are part of the major network, issue the network ip-address [subnet-mask] command in router configuration mode. The subnet-mask parameter, which is supported in later versions of Cisco IOS Software, allows you to run EIGRP only on certain interfaces that are part of the same major network.
EIGRP can be configured for other features, like Message Digest 5 (MD5) authentication, to accept routing information only from trusted neighbors, automatic and manual summarization of routes and equal and unequal cost load balancing. It can filter incoming and outgoing updates, as well as adjust the metric of transmitted and received routes.
Basic Configuration Example:
First go to router process mode, the process number should be same on all devices to form neighbor relationship between them.
R1#conf t
R1(config)#router eigrp 1
R1(config-router)#
Then if you have to run EIGRP on the interfaces,specify each network with wildcard mask for every interface:
R1(config-router)#network 10.1.1.0 0.0.0.3
R1(config-router)#network 1.1.1.1 0.0.0.0
Some of the command like EIGRP authentication, defining Bandwidth to control EIGRP packets or to define EIGRP next-hop that can be configure under interface mode as shown below:
R1(config)#int fa0/0
R1(config-if)#ip authentication mode eigrp 1 md5
R1(config-if)#ip authentication key-chain eigrp 1 cisco
R1(config-if)#ip bandwidth-percent eigrp 1 75
If you want to configure EIGRP for IPv6, you first need to define the IPv6 router process on the router and run EIGRP under interface mode as shown below
R1#conf t
R1(config)#ipv6 router eigrp 1
R1(config-rtr)#eigrp router-id 10.1.1.1
R1(config-rtr)#no shut
!
R1(config)#Interface f0/0
R1(config-if)#ipv6 enable
R1(config-if)#ipv6 eigrp 1
!
For more information on EIGRP configuration with examples, refer to these documents:
