Dell PowerConnect B-RX Configuration Manual page 275

The following commands configure static IP routes to the same destination, but with different
metrics. The route with the lowest metric is used by default. The other routes are backups in case
the first route becomes unavailable. The device uses the route with the lowest metric if the route is
available.
BigIron RX(config)# ip route 192.128.2.69 255.255.255.0 209.157.22.1
BigIron RX(config)# ip route 192.128.2.69 255.255.255.0 192.111.10.1 2
BigIron RX(config)# ip route 192.128.2.69 255.255.255.0 201.1.1.1 3
In this example, each static route has a different metric. The metric is not specified for the first
route, so the default (1) is used. A metric is specified for the second and third static IP routes. The
second route has a metric of two and the third route has a metric of 3. Thus, the second route is
used only of the first route (which has a metric of 1) becomes unavailable. Likewise, the third route
is used only if the first and second routes (which have lower metrics) are both unavailable.
For complete syntax information, refer to
Configuring standard static IP routes and interface or null static
routes to the same destination
You can configure a null0 or interface-based static route to a destination and also configure a
normal static route to the same destination, so long as the route metrics are different.
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:
•
•
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
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
53-1001986-01
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.
shows an example of two static routes configured for the same destination network. One
Configuring forwarding parameters
"Configuring a static IP route"
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on page 199.
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