Floating Static Route

A floating static route is a static route explicitly configured with an administrative distance (AD) higher than the dynamic routing protocol normally in use. Under normal conditions, the dynamic routing protocol’s route is preferred and the static route goes unused; it only becomes active automatically as a backup route if that route is ever lost for some reason.

How to Configure It

By explicitly specifying an administrative distance value at the end of the ip route command, you can configure a static route with a value higher than the default (1).

Router(config)# ip route 192.168.2.0 255.255.255.0 10.1.2.2 200

In this example, the static route for destination network 192.168.2.0/24 is explicitly given an administrative distance of 200, higher than the default (1) for an ordinary static route. As long as a route from the dynamic routing protocol normally in use (e.g., OSPF, with a default AD of 110) exists, that route has a lower AD and is preferred, so this floating static route is not adopted into the routing table.

Use Cases

Floating static routes are mainly used as a backup route (backup link) for a link running a dynamic routing protocol. When a failure on the primary link is detected, the dynamic routing protocol’s route disappears from the routing table, and the floating static route with the higher AD automatically becomes active.

For the default administrative distance values and a list of them by route source, see Administrative Distance (AD).

References

RFC	Title	Overview
RFC 1812	Requirements for IP Version 4 Routers	Defines requirements for IPv4 routers, including concepts related to route selection priority.