Static Routing

The term static routing denotes the use of manually configured or injected static routes for traffic forwarding purposes. Using a static route might be appropriate in the following circumstances:

■ When it is undesirable to have dynamic routing updates forwarded across slow bandwidth links, such as a dialup link

■ When the administrator needs total control over the routes used by the router

■ When a backup to a dynamically learned route is necessary

■ When it is necessary to reach a network that is accessible by only one path (a stub network)

Configuring and maintaining static routes is time-consuming. Properly implementing static routes requires complete knowledge of the entire network.

Figure 7-1 illustrates a stub network scenario in which the use of static routes is favored over a dynamic routing protocol. The right side of Figure 7-1 shows a stub network with a single entry/ exit point over the SO interface of Router A. On the stub network router (Router A), a static default route is configured so that the SO link forwards all traffic toward destinations outside the stub network. On Router B, a static route is installed toward the stub network and then is redistributed into the routing protocol so that reachability information for the stub network is available throughout the rest of the network.

Figure 7-1 Use Static Routes with a Stub Network

Figure 7-1 Use Static Routes with a Stub Network

Static Route to 192.168.1.0

172.16.2.2

Stub Network 192.168.1.0

172.16.2.2

Static Default Route

Stub Network 192.168.1.0

NOTE Static routes are unidirectional. A static route configured in one direction via one router must have a corresponding static route configured on the adjacent router, in the opposite direction, for the return path. Figure 7-1 includes these two routes.

By using static and default static routes in this scenario, no traffic from a dynamic routing protocol is present on the serial link or in the stub network. In addition, the processor and memory requirements for both routers are lower; in the stub network, a low-end router would suffice. Static routes are therefore appropriate in situations such as with stub networks, hub-and-spoke connections (also called star connections), and dialup environments.

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