TMS zl Management and Configuration Guide ST.1.2.100916

9-5
Routing
Static Routing
Floating Static Routes
As mentioned, a floating route is a route that the module knows but does not
currently exist in the module’s active routing table. Floating routes can be
created when the module learns too many routes. You can also create floating
routes deliberately.
A floating static route is generally used in conjunction with redundant GRE
tunnels. In this use model, two GRE tunnels offer a connection to the same
remote network. The TMS zl Module knows a route to the remote network
through the primary GRE tunnel interface. This route can be either static or
dynamic.
The module also requires a route to the remote network through the redundant
GRE tunnel in case the primary tunnel fails. Because you probably do not want
to send dynamic routing updates across a tunnel intended only for backup,
generally this route is a static route. In particular, it is a floating static route,
which appears in the routing table only when the route through the primary
GRE tunnel has been removed (because that tunnel has gone down). Config-
ure a static route as a floating static route as follows:
■ When the primary route is a static route, configure the administrative
distance of the floating static route as higher than that of the primary
route. Alternatively, if both routes have the same administrative distance,
you can configure the metric of the floating static route as higher than that
of the primary route.
■ When the primary route is a dynamic route, configure the administrative
distance of the floating static route as higher than that of the routing
protocol used on the primary tunnel interface.
This configuration ensures the module prefers the route through the primary
GRE tunnel interface when it is available. When the primary route is not
available, the floating static route will be added to the routing table, and the
redundant GRE tunnel will be used to access the remote network.