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7.2 | |
RIP | |
| 7.2.10 | |
Integrating static routes with RIP |
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Static routes are user-defined routes that
force packets moving between a source and a destination to take a
specific path. Static routes become very important if the Cisco IOS
software does not learn a route to a particular destination. They are
also useful for specifying a “gateway of last resort”, commonly
referred to as a default route. If a packet is destined for a subnet
that is not explicitly listed in the routing table, the packet is
forwarded to the default route.
A router running RIP can receive a default route via an update from another router running RIP. Another option is for the router to generate the default route itself. The static routes can be removed using
the
no ip route global configuration command. The administrator can
override a static route with dynamic routing information by adjusting
the administrative distance values. Each dynamic routing protocol has
a default administrative distance (AD). A static route can be defined
as less desirable than a dynamically learned route, as long as the AD
of the static route is higher than that of the dynamic route.
Static routes that point out an interface will be advertised via the RIP router that owns the static route, and propagated throughout the internetwork. This is because static routes that point to an interface are considered in the routing table to be connected and thus lose their static nature in the update. If a static route is assigned to an interface that is not defined in the RIP process, via a network command, RIP will not advertise the route unless a redistribute static command is specified in the RIP process. When an interface goes down, all static routes pointing out that interface are removed from the IP routing table. Likewise, when the software can no longer find a valid next hop for the address specified in the static route, then the static route is removed from the IP routing table. In Figure
To configure a static route, use the
Figure
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a static
route has been configured on the GAD router to take the place of the
RIP route in the event that the RIP routing process fails. This is
referred to as a floating static route. The floating static route was
configured by defining an AD on the static route (130) greater than
the default AD of RIP (120). The BHM router would also need to be
configured with a default route.
command in global configuration mode.
