Quick Reference Guide

602 PowerConnect B-Series TI24X Configuration Guide
53-1002269-02
Configuring IP parameters – Layer 3 Switches
21
• 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 99 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.
FIGURE 99 Standard and null static routes to the same destination network
Figure 100 shows another example of two static routes. In this example, a standard static route
and an interface-based static route are configured for destination network 192.168.6.0/24. The
interface-based static route has a lower metric than the standard static route. As a result, the
Layer 3 Switch always prefers the interface-based route when the route is available. However, if the
interface-based route becomes unavailable, the Layer 3 Switch still forwards the traffic toward the
destination using an alternate route through gateway 192.168.8.11/24.
FIGURE 100 Standard and interface routes to the same destination network
X
Two static routes to 192.168.7.0/24:
--Standard static route through
gateway 192.168.6.157, with metric 1
--Null route, with metric 2
Switch A
Switch A
Switch B
Switch B
192.168.6.188/24 192.168.6.157/24
192.168.7.7/24
192.168.7.69/24
When standard static route
is good, Switch A uses that
route.
192.168.6.188/24
192.168.6.157/24
192.168.7.7/24
192.168.7.69/24
If standard static route is
unavailable, Switch A uses
the null route (in effect dropping
instead of forwarding the packets).
Null