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| 5.2 |  | Troubleshooting Static Routes |
| 5.2.2 |  | Static routes and intermediate addresses |

Static routes can be created either by using an intermediate network address or an exit interface. In most cases, using an exit interface will be more efficient during the routing table process for resolving the static route. Figure shows a sample network with three routers.

Figure shows a static route being configured and installed in the routing table.

The static route that was created uses an intermediate IP address of 172.16.2.2. This is sometimes referred to as the next-hop IP address, but the IP address does not have to be the physical next-hop. As long as the intermediate IP address can be resolved in the routing table, it does not have to be the actual next-hop routers interface. Ultimately, the static network route, 172.16.3.0 in the example, must finally be resolved to a route in the routing table that has an exit interface.

Figure shows the routing table of RouterA after the static route was installed.

Notice that the static route that was configured does not contain an exit interface. Instead, the static routing table entry contains the intermediate address that was used when configuring the static route.

Whenever the routing table process needs to use the static route entry for the 172.16.3.0/24 network, it will also need to resolve the intermediate address, 172.16.2.2. This is called a recursive lookup.

Because this routing table entry for the 172.16.3.0/24 route does not contain an exit interface, but instead the intermediate address 172.16.2.2, it cannot use this entry alone to forward the packets. The routing table process uses the intermediate address of 172.16.2.2 and does another lookup (recursive lookup) in the routing table to find a route for this 172.16.2.0 network.

The routing table process finds the directly connected network entry for 172.16.2.0.

> C 172.16.2.0 is directly connected, Serial0/0

Because this entry does have an exit interface, Serial0/0, the routing table process can use this route to forward the packets for 172.16.3.0/24. Remember that it took two routing table lookups to route packets using the static route entry 172.16.3.0/24. The first routing table lookup was for the 172.16.3.0 network, the destination IP address of the packet, and the second routing table lookup was for the exit interface of the intermediate address used in the entry.

One additional route lookup may not be much of a factor on the performance of the routing process. However, static routes, which take multiple recursive lookups to get resolved, could have an impact.