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| 5.2 |  | Troubleshooting Static Routes |
| 5.2.3 |  | Static route optimization with serial networks |

There are ways to avoid recursive table lookups. Although, there may be times when recursive table lookups are preferred and configured by the network administrator.

Most of the time, static routes over serial point-to-point networks can easily avoid recursive route lookups by using an exit interface instead of the intermediate or next-hop address. Figure shows an example of creating a static route on RouterB for RouterA LAN, using an exit interface instead of an intermediate address.

Examine how this route was installed in the routing table, as shown in Figure .

Instead of using an intermediate address, this route is resolved with the exit interface, Serial0/0 that was configured with the static route command. The routing process, using this single entry, can forward any packets destined for the 172.16.1.0/24 network. No recursive route lookups are needed. Because only a single routing table lookup is needed, instead of multiple, recursive lookups, this type of static route will increase performance of the routing table process.

Notice that the routing table states that this static route is “directly connected.”

> S 172.16.1.0 is directly connected, Serial0/0

In the case of a static route, “directly connected” means that the static route was configured with an exit interface. This does not mean that it is a directly connected network of an interface on the router. Like all static routes, the default administrative distance of this static route is still 1. Only directly connected interfaces, which have a code of C in the routing table, can have an administrative distance of 0. Although it is possible to modify the administrative distance of static and dynamic routes, they cannot be given the administrative distance of 0. Likewise, directly connected interfaces can only have an administrative distance of 0.