Illustrated TCP/IP by Matthew G. Naugle Wiley Computer Publishing, John Wiley & Sons, Inc. ISBN: 0471196568   Pub Date: 11/01/98

Chapter 110
Authentication

There really is not room in the RIP update datagram for authentication. But since this has become commonplace (OSPF), room was made for it. The address family identifier (AFI) is used for authentication. If the AFI contains a 0xFFFF, then the first entry in the route entry list is the password to be used for authentication. The header of the RIP datagram changes as shown in the slide. The authentication type is type 2 (simple password) and the next 16 bytes contain this password (any amount of characters up to 16 bytes). RIPv1 will ignore this entry (the first entry), for the AFI is not set to an address family of IP.

If a RIPv2 router is configured with no authentication, it will accept and process both RIPv1 and v2 unauthenticated messages and discard authenticated messages.. If the RIPv2 router is configured for authentication, it will accept RIPv1 and v2 messages that pass authentication. Remember, not all v1 implementations follow the RFC. They may play with the fields and still be able to be processed by RIPv1 routers! This is not recommended. Unauthenticated RIPv2 messages will be discarded.

Authentication