The network administrators use floating static routes to provide a backup path to a primary static or dynamic route, in the event of a link failure. The floating static route works only when the primary route is not available. There may be the primary route fails due to physical layer problems and a wrong configuration, or many other reasons. If there are multiple routes available to the destination, the router will choose the path with the lowest administrative distance. Remember that Administrative distance determines the trustworthiness of a route. If multiple paths exist to the destination, the router will choose the route with the lowest administrative distance value.
The default administrative distance of EIGRP is 90, so if we want to configure the floating static route for EIGRP routes. The floating static route must be configured with an administrative value higher than 90. If the floating static route is configured with a lower value than 90, the router will use that static route first.
In the figure above, the host has two paths to reach a web server.
Router3 has two default static routes configured, one with the default value of administrative distance and other with an administrative distance of 3. Router3 typically send data to the web server via Router1, because the static route pointing to Router1 is configured with default AD value (1). The route pointing to router2 is configured with AD value of 3, So this is the static floating route.
When there is a problem in the first path, the router should automatically delete the first route from the routing table and add the floating static route in the routing table. So, the traffic will flow to the web server via the floating route. The administrative distance value of common protocol is the following:
- Static – 1
- EIGRP = 90
- IGRP = 100
- OSPF = 110
- IS-IS = 115
- RIP = 120
Configure Floating Static Route
We can configure the static route using the “ip route” command in global configuration. If the administrative distance is not specified, the default value is (1). For example, in the above topology, the default static route is configured with its default administrative distance and pointing to Fast Ethernet 0/0 of Router3. So the static floating route should be configured using the following command in global configuration mode.
- Router3#configure terminal
- Router3(config)#ip route 0.0.0.0 0.0.0.0 FastEthernet 0/1 3
Verify the Floating Static Route
Router3 has default static route pointing to Router1 with default administrative distance and the floating static route pointing to Router1 with AD value of (3). So, this value is greater than the default value of 1 and, as a result, this route floats and not present in the routing table, unless the preferred route fails. So, we can use the “show ip route” command. The following image verifies the default route configured from Router 1 to Router 3 in the routing table. The floating route is not present in the routing table.
We can verify the route using “tracert and traceroute” command also. I can also verify the floating static route by disconnecting the cable between Router1 and Router3. And then I can check the routing table of Router3. The figure below illustrates the routing table when I remove the cable between Router3 and Router1.