Dell PowerConnect B-RX BigIron RX Series Configuration Guide v02.8.00 - Page 281

Configuring forwarding parameters 7 When the device has multiple routes to the same destination, the device always prefers the route with the lowest metric. Generally, when you configure a static route to a destination network, you assign the route a low metric so that the device prefers the static route over other routes to the destination. This feature is especially useful for the following configurations. These are not the only allowed configurations but they are typical uses of this enhancement: • When you want to ensure that if a given destination network is unavailable, the device drops (forwards to the null interface) traffic for that network instead of using alternate paths to route the traffic. In this case, assign the normal static route to the destination network a lower metric than the null route. • When you want to use a specific interface by default to route traffic to a given destination network, but want to allow the device to use other interfaces to reach the destination network if the path that uses the default interface becomes unavailable. In this case, give the interface route a lower metric than the normal static route. NOTE You cannot add a null or interface-based static route to a network if there is already a static route of any type with the same metric you specify for the null or interface-based route. Figure 11 shows an example of two static routes configured for the same destination network. One of the routes is a standard static route and has a metric of 1. The other static route is a null route and has a higher metric than the standard static route. The device always prefers the static route with the lower metric. In this example, the device always uses the standard static route for traffic to destination network 192.168.7.0/24, unless that route becomes unavailable, in which case the device sends traffic to the null route instead. BigIron RX Series Configuration Guide 205 53-1002253-01