Foundry Networks Switch and Router Installation And Configuration Manual page 486

Foundry Switch and Router Installation and Configuration Guide
The <ip-mask> parameter specifies the network mask. Ones are significant bits and zeros allow any value. For
example, the mask 255.255.255.0 matches on all hosts within the Class C sub-net address specified by <ip-
addr>. Alternatively, you can specify the number of bits in the network mask. For example, you can enter
209.157.22.0/24 instead of 209.157.22.0 255.255.255.0.
The null0 parameter indicates that this is a null route. You must specify this parameter to make this a null route.
The <metric> parameter adds a cost to the route. You can specify from 1 – 16. The default is 1.
The distance <num> parameter configures the administrative distance for the route. You can specify a value from
1 – 255. The default is 1. The value 255 makes the route unusable.
NOTE: The last two parameters are optional and do not affect the null route, unless you configure the
administrative distance to be 255. In this case, the route is not used and the traffic might be forwarded instead of
dropped.
USING THE WEB MANAGEMENT INTERFACE
You cannot configure a null IP static route using the Web management interface.
Configuring Load Balancing and Redundancy Using Multiple Static Routes to the Same
Destination
You can configure multiple static IP routes to the same destination, for the following benefits:
• IP load sharing – If you configure more than one static route to the same destination, and the routes have
different next-hop gateways but have the same metrics, the Layer 3 Switch load balances among the routes
using basic round-robin. For example, if you configure two static routes with the same metrics but to different
gateways, the Layer 3 Switch alternates between the two routes. For information about IP load balancing,
see "Configuring IP Load Sharing" on page 15-51.
• Backup Routes – If you configure multiple static IP routes to the same destination, but give the routes
different next-hop gateways and different metrics, the Layer 3 Switch will always use the route with the lowest
metric. If this route becomes unavailable, the Layer 3 Switch will fail over to the static route with the next-
lowest metric, and so on.
NOTE: You also can bias the Layer 3 Switch to select one of the routes by configuring them with different
administrative distances. However, make sure you do not give a static route a higher administrative distance than
other types of routes, unless you want those other types to be preferred over the static route. For a list of the
default administrative distances, see "Changing Administrative Distances" on page 19-33.
The steps for configuring the static routes are the same as described in the previous section. The following
sections provide examples.
USING THE CLI
To configure multiple static IP routes, enter commands such as the following.
BigIron(config)# ip route 192.128.2.69 255.255.255.0 209.157.22.1
BigIron(config)# ip route 192.128.2.69 255.255.255.0 192.111.10.1
The commands in the example above configure two static IP routes. The routes go to different next-hop gateways
but have the same metrics. These commands use the default metric value (1), so the metric is not specified.
These static routes are used for load sharing among the next-hop gateways.
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 Layer 3 Switch uses the route with the lowest metric if the route is available.
BigIron(config)# ip route 192.128.2.69 255.255.255.0 209.157.22.1
BigIron(config)# ip route 192.128.2.69 255.255.255.0 192.111.10.1 2
BigIron(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
15 - 44 December 2000