Floating static routes are static routes that have an administrative distance greater than the administrative distance of another static route or dynamic routes. They are very useful when providing a backup to a primary link, as shown in the figure.
By default, static routes have an administrative distance of 1, making them preferable to routes learned from dynamic routing protocols. For example, the administrative distances of some common dynamic routing protocols are:
- EIGRP = 90
- IGRP = 100
- OSPF = 110
- IS-IS = 115
- RIP = 120
The administrative distance of a static route can be increased to make the route less desirable than that of another static route or a route learned through a dynamic routing protocol. In this way, the static route “floats” and is not used when the route with the better administrative distance is active. However, if the preferred route is lost, the floating static route can take over, and traffic can be sent through this alternate route.
A floating static route can be used to provide a backup route to multiple interfaces or networks on a router. It is also encapsulation independent, meaning it can be used to forward packets out any interface, regardless of encapsulation type.
An important consideration of a floating static route is that it is affected by convergence time. A route that is continuously dropping and re-establishing a connection can cause the backup interface to be activated unnecessarily.