Brocade Virtual ADX Switch and Router Guide (Supporting ADX v03.1.00) - Manual (Page 87)

Brocade Virtual ADX Switch and Router Guide 73
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Configuring IP parameters
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For complete syntax information, refer to “Configuring a static IP route” on page 70.
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 Virtual ADX has multiple routes to the same destination, the Virtual ADX 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 Virtual ADX 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 feature:
• When you want to ensure that if a given destination network is unavailable, the Virtual ADX
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 Virtual ADX 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 16 shows an example of two static routes configured for the same destination network. In
this example, 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 Virtual ADX always
prefers the static route with the lower metric. In this example, the Virtual ADX 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 Virtual ADX sends traffic to the null route instead.