10.5 RIP Version 2

RFC 1388 [Malkin 1993a] defines newer extensions to RIP, and the result is normally called RIP-2. These extensions don't change the protocol, but pass additional information in the fields labeled "must be zero" in Figure 10.3. RIP and RIP-2 can interoperate if RIP ignores the fields that must be zero.

Figure 10.10 is a redo of that figure, as defined by RIP-2. The version is 2 for RIP-2.

Figure 10.10. Format of a RIP-2 message.

The routing domain is an identifier of the routing daemon to which this packet belongs. In a Unix implementation this could be the daemon's process ID. This field allows an administrator to run multiple instances of RIP on a single router, each operating within one routing domain.

The route tag exists to support exterior gateway protocols. It carries an autonomous system number for EGP and BGP.

The subnet mask for each entry applies to the corresponding IP address. The next -hop IP address is where packets to the corresponding destination IP address should be sent. A value of 0 in this field means packets to the destination should be sent to the system sending the RIP message.

A simple authentication scheme is provided with RIP-2. The first 20-byte entry in a RIP message can specify an address family of 0xffff, with a route tag value of 2. The remaining 16 bytes of the entry contain a cleartext password.

Finally, RIP-2 supports multicasting in addition to broadcasting (Chapter 12). This can reduce the load on hosts that are not listening for RIP-2 messages.