IP static routes remain in the IP route table only as long as the port or virtual interface used by the route is available and the next-hop IP address is valid.
If the interface is not available and the next-hop IP address is invalid, the software removes the static route from the route table. When the port or virtual routing interface becomes available and the next-hop is valid, the software adds the route to the route table.
This feature allows the router to adjust to changes in network topology. The router does not continue trying to use routes on unavailable paths but instead uses routes only when their paths are available.
In the following example, a static route is configured on Switch A.
In the example, the static route to the 207.95.7.0 destination was configured as follows, using 207.95.6.157 as the next-hop gateway.
device(config)# ip route 207.95.7.0/24 207.95.6.157
When you configure a static IP route, you specify the destination address for the route and the next-hop gateway or Layer 3 interface through which the Layer 3 device can reach the route. The device adds the route to the IP route table. In this case, Switch A knows that 207.95.6.157 is reachable through port 1/2, and also assumes that local interfaces in that subnet are on the same port. Switch A deduces that IP interface 207.95.7.7 is also on port 1/2.