Next Hop Identification

The inclusion of a Next Hop identification field helped make RIP-2 more efficient than RIP by preventing unnecessary hops. This feature is particularly effective for network environments using multiple routing protocols simultaneously. This is because with multiple, dissimilar routing protocols, it is possible that some routes may never be discovered.

• Consider a scenario in which there is a large-sized company with a corporate data center and an internal IP WAN (an intranet), for example. Instead of examining the entire intranet, an example using just two work locations within this intranet should suffice. Each location has its own LAN and router. (Router 1 connects network 193.168.125.0 to the company's IP WAN, and Router 2 connects network 193.168.124.0.) These two routers are interconnected via a T1 to an older router (Router 3) in the intranet's backbone. This company has elected to use RIP-2 between the work location routers and the backbone. EIGRP is used for route calculations between the backbone routers and the data centers. The older backbone router, Router 3, is being phased out. This router is connected to the intranet backbone with an ancient 56 kbps leased line. Although originally a wise and economical selection, this transmission facility is now obsolete and impedes traffic flows in the intranet. The new router, Router 4, is physically co-located with Router 3, and the two are interconnected via a FDDI ring. Router 4 is also connected to the backbone router with a T3 leased line. Figure 9-5 illustrates this network.

Figure 9-5: A network diagram for a next hop example.

Figure 9-5: A network diagram for a next hop example.

The company's use of two different routing protocols creates the potential for routing problems during the migration to Router 4 and its T3. This router connects only to other routers in the intranet's backbone. Therefore, all its ports have been configured to use EIGRP. Because it is not running RIP-2, or even RIP, the work location Routers 1 and 2 can't learn of its existence. As a result, the T3 route won't be discovered or used by the networks connected to Routers 1 and 2.

Figure 9-6 depicts this.

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