Configuration Guide User guide

996 FastIron Configuration Guide
53-1002494-02
Configuring IP parameters – Layer 3 Switches
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, refer to “Configuring IP load sharing”
on page 1001.
• 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, refer to “Administrative distance” on
page 1265.
The steps for configuring the static routes are the same as described in the previous section. The
following sections provide examples.
To configure multiple static IP routes, enter commands such as the following.
Brocade(config)# ip route 192.128.2.69 255.255.255.0 209.157.22.1
Brocade(config)# ip route 192.128.2.69 255.255.255.0 192.111.10.1
The commands in the previous example 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.
Brocade(config)# ip route 192.128.2.69 255.255.255.0 209.157.22.1
Brocade(config)# ip route 192.128.2.69 255.255.255.0 192.111.10.1 2
Brocade(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 a static IP route” on page 993.