This KB explains how to configure the different IS-IS authentication options.

To configure IS-IS authentication, you must define an authentication password and specify the authentication type.

You can configure one of the following authentication methods:

• 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 recommend that you do not use this authentication method because it is insecure (the text can be “sniffed”).
• HMAC-MD5 authentication—Uses an iterated cryptographic hash function. The receiving routing device uses an authentication key (password) to verify the packet.S

Simple:

# set protocols isis level <1-2> authentication-type simple authentication-key <password>

MD5:

# set protocols isis interface <interface> level <1-2> hello-authentication-key-chain <key-chain-name>

# set security authentication-key-chains key-chain <key-chain-name> key <key identifier 0-63> secret <password>

# set security authentication-key-chains key-chain <key-chain-name> key <key identifier 0-63> start-time "2024-6-16.17:00:00 -0700"

# set security authentication-key-chains key-chain <key-chain-name> key <key identifier 0-63> algorithm md5

# set security authentication-key-chains key-chain <key-chain-name> key <key identifier 0-63> options isis-enhanced

The above information has to match for the adjacency to be established.

Execute the following commands to ensure that all ISIS adjacencies are up and authentication is working: 

> show isis adjacency 

> show isis authentication 

> show isis interface