The Cisco implementation of RIPv2 supports two modes of authentication: plain text and MD5 authentication.
Plain text authentication is the default setting in every RIPv2 packet, when authentication is enabled.
Plain text authentication should not be used when security is an issue, because the unencrypted authentication password is sent in every RIPv2 packet.
To configure RIPv2 authentication between two routers you need to carry out these steps.
1. Define a key chain with a name
2. Define the key or keys on the chain
3. Specify password or key chain
4. Enable authentication on the interface and specify the key chain to be used
5. Specify if the interface will use plain text or MD5
6. Configure Key Management – This is optional
Now configure the same on the remote end of the link to restore connectivity