A null static route sends network
traffic to a null interface, where the network packets are discarded.
About this task
You can use a null static route to handle traffic that should not be forwarded
because the preferred route is unavailable. The following figure depicts how a null
static route works with a standard route to the same destination.
Null route and standard
route to same destination
Procedure
Access global configuration
mode.
device# configure terminal
Configure the preferred route to a destination.
device(config)# ip route 192.168.7.0/24 192.168.6.157
This example creates a static route to destination network addresses that have an IP address beginning with 192.168.7.0. These destinations are routed through the next-hop gateway 192.168.6.157. The route carries the default metric of 1.
Configure a route to the same destination, followed by the keyword
null, a space, and a zero. On the same line, enter a cost metric that is higher than the metric for the preferred route.
device(config)# ip route 192.168.7.0/24 null 0 2
This example creates a null static route to the same destination. The metric is set higher so that the preferred route is used if it is available. When the preferred route becomes unavailable, the null route is used, and traffic to the destination is dropped.
Example
The following example summarizes the commands in
this procedure.
device# configure terminal
device(config)# ip route 192.168.7.0/24 192.168.6.157
device(config)# ip route 192.168.7.0/24 null 0 2
