EIGRP
Configuring Cisco’s routing protocol EIGRP to use authentication follows similar
steps as configuring RIP v2 authentication:
1. Enable EIGRP authentication on each interface with the ip authentication mode
eigrp command.
2. Define the key chain to use under each interface with the ip authentication key-
chain eigrp command.
3. Create the key chain specified in the previous step:
a. Define a key chain with the key chain command.
b. Identify the number of this authentication key with the key command.
c. Configure the actual authentication key with the key-string command.
Assuming your autonomous system number is 10, you would enable EIGRP authen-
tication on the interfaced FastEthernet 0/0, Serial 0/0, and Serial 0/1 with:
RouterOne#config terminal
Enter configuration commands, one per line. End with CNTL/Z.
RouterOne(config)#interface FastEthernet 0/0
RouterOne(config-if)#ip authentication mode eigrp 10 md5
RouterOne(config-if)#ip authentication key-chain eigrp 10 Chain1
RouterOne(config-if)#exit
RouterOne(config)#interface Serial 0/0
RouterOne(config-if)#ip authentication mode eigrp 10 md5
RouterOne(config-if)#ip authentication key-chain eigrp 10 Chain1
RouterOne(config-if)#exit
RouterOne(config)#interface Serial 0/1
RouterOne(config-if)#ip authentication mode eigrp 10 md5
RouterOne(config-if)#ip authentication key-chain eigrp 10 Chain1
RouterOne(config-if)#exit
RouterOne(config)#^Z
After your interfaces are configured to use EIGRP authentication, you then define the
key chain and the authentication key. The previous commands specify Chain1 as the
key chain to use for authentication, so the key chain command needs to be used to
create Chain1. In the following example, the authentication key 1 is defined as
UnguessableKey:
RouterOne#config terminal
Enter configuration commands, one per line. End with CNTL/Z.
RouterOne(config)#key chain Chain1
RouterOne(config-keychain)#key 1
RouterOne(config-keychain-ke)#key-string UnguessageKey
RouterOne(config-keychain-ke)#^Z
Perform this same configuration on all other routers and interfaces that require
EIGRP authentication to complete the setup.
