Brocade Communications Systems Layer 3 Routing Configuration ICX 6650 - Manual (Page 69)

Brocade ICX 6650 Layer 3 Routing Configuration Guide 51
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Configuring IP parameters – Layer 3 Switches
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 Layer 3 Switch
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 Layer 3 Switch 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 5 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 Layer 3 Switch always
prefers the static route with the lower metric. In this example, the Layer 3 Switch 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 Layer 3 Switch sends traffic to the null route instead.