Floating Static Routes

Floating static routes are an enhancement to static routes that use administrative distance to appropriately weight the backup route in relation to routes learned through dynamic routing protocols.

Floating Static Routes

R4(config)# ip route bri0/0 200 R4(config)# ip route bri0/0 200

Floating static routes are static routes with an administrative distance (AD) greater than dynamically learned routes

AD = 20

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When ISDN is implemented in the real world, it is usually with the use of floating static routes. Floating static routes are static routes that have an Administrative Distance (AD) greater than the administrative distance of dynamically learned routes. An Administrative Distance can be assigned to a static route so that the static route is less desirable than a dynamic route. In this manner, the static route is not used when the dynamic route is available. However, if the dynamic route is lost, the static route can take over, and traffic can be sent through this alternate route. If this alternate route is provided using a Dial-on-Demand Routing (DDR) interface, then the DDR interface can be used as a backup mechanism.

Implementing floating static routes is quick, simple, and easy to test. If your primary link is routing data for the and networks, you can implement floating static routes as follows:

R4(config)# ip route bri0/0 200

R4(config)# ip route bri0/0 200

If R4 ever loses its dynamically learned routes, which should have an administrative distance less than 200, the floating static routes will come into effect and route traffic over the bri0/0 circuit. If and when the dynamically learned routes enter the routing table again, due to their lower AD, they will be the preferred entries once again.

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