Advantages of dynamic routing
Scott M. Ballew
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In a previous tip, we talked about the advantages of static routing. But dynamic routing has its advantages as well, and they may outweigh static routing's benefits. This tip, excerpted from Managing IP Networks with Cisco Routers, gives details.
The chief advantages of dynamic routing over static routing are scalability and adaptability. A dynamically routed network can grow more quickly and larger, and is able to adapt to changes in the network topology brought about by this growth or by the failure of one or more network components.
With a dynamic router protocol, routers learn about the network topology by communicating with other routers. Each router announces its presence, and the routes it has available, to the other routers on the network. Therefore, if you add a new router, or add an additional segment to an existing router, the other routers will gear about the addition and adjust their routing tables accordingly. You don't have to reconfigure the routers to tell them that the network has changes. Similarly, if you move a network segment, the other routers will hear about the change. You only need to change the configuration of the router (or routers) that connect the segment that moved. This reduces the chance that errors will occur.
The ability to learn about changes to the network's configuration has implications beyond adding new segments or moving old ones. It also means that the network can adjust to failures. If a network has redundant paths, then a partial network failure appears to the routers as if some segments got moved (they are now reached via alternate paths), and some segments have been removed from the network (they are now unreachable). In short, there's no real difference between a network failure and a configuration change. Dynamic routing allows the network to continue functioning, perhaps in a degraded fashion, when partial failure occurs.
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