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| 3.3 |  | Floating Static Routes |
| 3.3.1 |  | Configuring floating static routes |

One of the disadvantages of static routing is that it cannot adapt to topology changes. However, static routing can be configured to have limited adaptability by creating floating static routes.

Floating static routes are static routes configured with an administrative distance value that is greater than that of the primary route or routes. Floating static routes are fallback routes, or backup routes, that do not appear in the routing table until another route to the same destination fails. Assume that RTB is connected to network 10.0.0.0/8 through two different links. Additionally, that the RTB preferred route to network 10.0.0.0/8 is through RTC because that link has a higher bandwidth. This route is learned by RIP. RTB should use the slower link to 10.0.0.0/8 through RTA, only if the primary route fails. The route to RTA is statically configured.

A floating static route must be used to statically configure RTB, so that it will use the slower link to reach 10.0.0.0/8 after the RIP route fails.

> RTB(config)#ip route 10.0.0.0 255.0.0.0 1.1.1.1 130

This

ip route command includes an administrative distance of 130. Recall that static routes have a default administrative distance of 1. To create a floating static route, the administrative distance value must be manually configured. This value must be greater than the primary route administrative distance value. In this example, the primary route is learned by RIP and has an administrative distance of 120. By configuring the static route with an administrative distance of 130, the static route will be less desirable than the primary route. The RIP route through RTC is preferred. However, if the RIP route is lost, the floating static route takes its place in the routing table.

Floating static routes can be used in conjunction with other static routes to create a semi-adaptable static routing scheme.

> RTZ(config)#ip route 0.0.0.0 0.0.0.0 s0
> RTZ(config)#ip route 0.0.0.0 0.0.0.0 s1 5
> RTZ(config)#ip route 4.0.0.0 255.0.0.0 s2
> RTZ(config)#ip route 4.0.0.0 255.0.0.0 s3 5
> RTZ(config)#ip route 4.0.0.0 255.0.0.0 s4 10

If RTZ is configured with these commands, it installs one route to 0.0.0.0/0 using S0, and one route to 4.0.0.0/8, using S2. If S0 becomes unavailable, RTZ will install the floating static route to 0.0.0.0/0, using S1, into its routing table. If S2 fails, RTZ will go back to using S3 to reach 4.0.0.0/8. Finally, if both S2 and S3 go down, RTZ will use the least desirable static route to 4.0.0.0/8, with an administrative distance 10.

| Lab Activity e-Lab Activity: Configuring Floating Static Routes This lab is to create multiple floating static routes.