Integrated Routing Protocols

One approach to supporting multiple routing protocols is to use a single, integrated routing protocol. An integrated protocol is simultaneously capable of routing two different protocols and addresses. Examples of this form of routing protocol are the emerging series of ng protocols that are designed to facilitate the migration between IPv4 and IPv6. Specific examples of integrated protocols are OSPFng and RIPng and RIP Version 2 (RIP-2). RIP-2 was designed to be fully backward compatible with RIP Version 1. Therefore, it qualifies as an integrated routing protocol.

Using an integrated routing protocol provides a seamless integration of different routing protocols. The one drawback to this approach is that there are so few integrated routing protocols! Most (if not all) such protocols are nothing more than advanced versions of routing protocols that are backward compatible with their earlier versions. As such, they are transitional mechanisms that facilitate a graceful migration from one version of a routing protocol to the next. In theory, the entire network will eventually be converted to using the newest version of the protocol. After the transition is complete, therefore, the integration features of the routing protocol become moot. However, the network benefits from the expanded capability set of the new version of the protocol.

Figure 14-5 demonstrates a small RIP network that is being upgraded, in sections, to RIP-2. Portions of the network are still using RIP. The migration began with upgrading the gateway router to RIP-2. Each of the subnetworks can then be upgraded to RIP-2 without disrupting service across the network.

Figure 14-5: Networks with multiple routing protocols may use an integrated routing protocol, such as RIP-2.

Figure 14-5: Networks with multiple routing protocols may use an integrated routing protocol, such as RIP-2.

Networks using an integrated routing protocol, unlike networks using any of the other mechanisms for supporting dual routing protocols, function as a single network. There is no need to convert datagrams, translate addresses, or redistribute routing information between the old protocol and the new, integrated protocol. Interoperability between RIP and RIP-2, for example, is a native function of RIP-2. The only functional limitation is that routers still running the older version of the RIP cannot benefit from any of the features added to RIP-2.

Other integrated protocols exist, too. Some examples include IS-IS, which can carry both DECnet and IP, and Cisco's EIGRP, which can share routing information with IGRP networks. Selecting an integrated routing protocol is a matter of understanding your particular requirements. You may find one that fits your needs perfectly, or you may discover that none of the available integrated protocols will work in your particular situation.

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