22-61
Catalyst 3550 Multilayer Switch Software Configuration Guide
78-11194-03
Chapter22 Configuring IP Unicast Routing Configuring Protocol-Independent Features
Filtering Routing Information
You can filter routing protocol information by performing the tasks described in this section.
Note When routes are redistributed between OSPF processes, no OSPF metrics are preserved.

Setting Passive Interfaces

To prevent other routers on a local network from dynamically learning abou t ro ut es , you c an us e th e
passive-interface router configuration command to keep routing update messa ges fr om bei ng sent
through a router interface. When you use this command in the OSPF protocol, the interface address you
specify as passive appears as a stub network in the OSPF domain. OSPF routing information is neither
sent nor received through the specified router interface.
In networks with many interfaces, to avoid having to m anua lly set the m a s pa ssive , you c a n s et all
interfaces to be passive by default by using the passive-interface default router configuration command
and manually setting interfaces where adjacencies are desired.
Beginning in privileged EXEC mode, follow these steps to configur e pa ssive i nte rfac es :
Use a network monitoring privileged EXEC command such as show ip ospf interface to verify the
interfaces that you enabled as passive, or use the show ip interface privileged EXEC command to veri fy
the interfaces that you enabled as active.
To re-enable the sending of routing updates, use the no passive-interface interface-id router
configuration command. The default keyword sets all interfaces as passive by defa ult. You can then
configure individual interfaces where you want adjacenc ies by using the no passive-interface rout er
configuration command. The default keyword is useful in Internet ser vice provider and large enterprise
networks where many of the distribution routers have more than 200 interfaces.
Command Purpose
Step1 configure terminal Enter global configuration mode.
Step2 router {rip | ospf | igrp | eigrp} Enter router configuration mode.
Step3 passive-interface interface-id Suppress sending routing updates through the specified Layer 3
interface.
Step4 passive-interface default (Optional) Set all interfaces as passive by default.
Step5 no passive-interface interface type (Optional) Activate only those interfaces that need to have
adjacencies sent.
Step6 network network-address (Optional) Specify the list of networks for the routing process. The
network-address is an IP address.
Step7 end Return to privileged EXEC mode.
Step8 copy running-config startup-config (Optional) Save your entries in the configuration file.