To define an authentication, a key chain needed to enable authentication for routing protocols. To enter key-chain configuration mode, use the `key chain` command in global configuration mode. Only DRP Agent, Enhanced Interior Gateway Routing Protocol (EIGRP), and Routing Information Protocol (RIP) Version 2 use key chains.

It is useful to have multiple keys on a key chain so that the software can sequence through the keys as they become invalid after time, based on the accept-lifetime and send-lifetime key chain key command settings. If the last key expires, authentication will continue and an error message will be generated. To disable authentication, you must manually delete the last valid key

key chain commandkey chain name-of-chain
no key chain name-of-chain 

Configuration example

key chain MD5
key 1
  key-string MD5HASH
  accept-lifetime 13:30:00 Jan 25 1996 duration 7200
  send-lifetime 14:00:00 Jan 25 1996 duration 3600
key chain TEXT
key 1
  key-string CLEARTEXT
key 2
  key-string KEY2