IS-IS Authentication MD5

You can authenticate all IS-IS protocol exchanges to guarantee that only trusted routing devices participate in the autonomous system (AS) routing. By default, IS-IS authentication is disabled on the routing device. To configure IS-IS authentication, you must specify an authentication password and the authentication type. 

You can use the following authentication methods with IS-IS: 

• Simple authentication-Uses a text password that is included in the transmitted packet. The receiving routing device uses an authentication key (password) to verify the packet. Simple authentication is included for compatibility with existing IS-IS implementations. However, we do not recommend this authentication method because it is insecure (password, being cleartext, can be easily "sniffed"). 
• HMAC-MD5 authentication-Uses an iterated cryptographic hash function. The receiving routing device uses an authentication key (password) to verify the packet. This feature introduces HMAC-MD5 IS-IS authentication.