NOTE
You also can bias the Layer 3 switch to select one of the routes by conguring them with dierent 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.
The steps for conguring the static routes are the same as described in the previous section. The following sections provide examples.
To congure multiple static IP routes, enter commands such as the following.
device(config)# ip route 10.128.2.69 255.255.255.0 10.157.22.1
device(config)# ip route 10.128.2.69 255.255.255.0 10.111.10.1
The commands in the previous example congure two static IP routes. The routes go to dierent next-hop gateways but have the same
metrics. These commands use the default metric value (1), so the metric is not specied. These static routes are used for load sharing
among the next-hop gateways.
The following commands congure static IP routes to the same destination, but with dierent metrics. The route with the lowest metric is
used by default. The other routes are backups in case the rst route becomes unavailable. The Layer 3 switch uses the route with the
lowest metric if the route is available.
device(config)# ip route 10.128.2.69 255.255.255.0 10.157.22.1
device(config)# ip route 10.128.2.69 255.255.255.0 10.111.10.1 2
device(config)# ip route 10.128.2.69 255.255.255.0 10.1.1.1 3
In this example, each static route has a
dierent metric. The metric is not specied for the rst route, so the default (1) is used. A metric is
specied 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 rst route (which has a metric of 1) becomes unavailable. Likewise, the third route is used only if the rst
and second routes (which have lower metrics) are both unavailable.
Conguring standard static IP routes and interface or null static routes to the same destination
You can
congure a null0 or interface-based static route to a destination and also congure a normal static route to the same destination,
so long as the route metrics are dierent.
When the Layer 3 switch has multiple routes to the same destination, the Layer 3 switch always prefers the route with the lowest metric.
Generally, when you congure a static route to a destination network, you assign the route a low metric so that the Layer 3 switch prefers
the static route over other routes to the destination.
This feature is especially useful for the following congurations. These are not the only allowed congurations 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) trac for that network instead of using alternate paths to route the trac. 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 specic interface by default to route trac 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.
In the example, two static routes congured for the same destination network. 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 trac to destination
network 192.168.7.0/24, unless that route becomes unavailable, in which case the Layer 3 switch sends trac to the null route instead.
Conguring IP parameters - Layer 3 switches
FastIron Ethernet Switch Layer 3 Routing
68 53-1003627-04
To Next Page
Loading...
Need help?
General
