Authenticate Cisco EIGRP routers
To help prevent unauthorized routing updates, EIGRP can be configured to authenticate peers.
For this example, two routers, A and B, are directly connected with Fast Ethernet. IP network is 10.1.1.0/24
Enter the appropriate passwords, then enter configuration mode:
Address the interfaces.
Router A:
ip address 10.1.1.1 255.255.255.0
Router B:
ip address 10.1.1.2 255.255.255.0
Configure EIGRP (same on both routers):
network 10.0.0.0
Then, create keychains in both routers.
Router A:
key 1
key-string 123
accept-lifetime infinite
send-lifetime 00:00:01 1 Jan 2004 23:59:59 1 Jan 2005
exit
key 2
key-string abc
accept-lifetime infinite
send-lifetime 00:00:01 1 Jan 2004 23:59:59 1 Jan 2005
Router B:
key 1
key-string 123
accept-lifetime infinite
send-lifetime 00:00:01 1 Jan 2004 23:59:59 1 Jan 2005
exit
key 2
key-string abc
accept-lifetime infinite
send-lifetime 00:00:01 1 Jan 2004 23:59:59 1 Jan 2005
Now, configure authentication . EIGRP Autonomous System number is 100.
Router A:
ip authentication mode eigrp 100 md5
ip authentication key-chain eigrp 100 rtrA
Router B:
ip authentication mode eigrp 100 md5
ip authentication key-chain eigrp 100 rtrB
Now the routers should be verifying the MD5 hash of EIGRP packets, dropping any that do not pass the verification.
In the key configuration, the "infinite" keyword can be used to make non-expiring keys. I would recommend the last keypair be non-expiring, to prevent network downtime if the administrator forgets to update the keys before they expire!
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