Brocade Virtual ADX Switch and Router Guide (Supporting ADX v03.1.00) - Manual (Page 90)

76 Brocade Virtual ADX Switch and Router Guide
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Configuring IP parameters
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Configuring a default network route
The Virtual ADX enables you to specify a candidate default route without the need to specify the
next hop gateway. If the IP route table does not contain an explicit default route (for example,
0.0.0.0/0) or propagate an explicit default route through routing protocols, the software can use
the default network route as a default route instead.
When the software uses the default network route, it also uses the default network route's next hop
gateway as the gateway of last resort.
This feature is especially useful in environments where network topology changes can make the
next hop gateway unreachable. This feature allows the Virtual ADX to perform default routing even
if the default network route's default gateway changes.
The feature thus differs from standard default routes. When you configure a standard default
route, you also specify the next hop gateway. If a topology change makes the gateway unreachable,
the default route becomes unusable.
For example, if you configure 10.10.10.0/24 as a candidate default network route, if the IP route
table does not contain an explicit default route (0.0.0.0/0), the software uses the default network
route and automatically uses that route's next hop gateway as the default gateway. If a topology
change occurs and as a result the default network route's next hop gateway changes, the software
can still use the default network route. To configure a default network route, use the following CLI
method.
If you configure more than one default network route, the Virtual ADX uses the following algorithm
to select one of the routes.
1. Use the route with the lowest administrative distance.
2. If the administrative distances are equal:
• Are the routes from different routing protocols? If so, use the route with the lowest IP
address.
• If the routes are from the same routing protocol, use the route with the best metric. The
meaning of “best” metric depends on the routing protocol:
Configuring a default network route
To configure a default network route, use one of the following methods. You can configure up to
four default network routes.
To configure a default network route, enter commands such as the following.
Virtual ADX(config)# ip default-network 10.157.22.0
Virtual ADX(config)# write memory
Syntax: ip default-network ip-addr
The ip-addr parameter specifies the network address.
To verify that the route is in the route table, enter the following command at any level of the CLI.