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Catalyst 3750-E and 3560-E Switch Software Configuration Guide
OL-9775-08
Chapter 40 Configuring IP Unicast Routing
Configuring Protocol-Independent Features
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 about routes, you can use the
passive-interface
router configuration command to keep routing update messages from being 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 manually set them as passive, you can set 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 configure passive interfaces:
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 verify
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 default. You can then
configure individual interfaces where you want adjacencies by using the
no passive-interface
router
configuration command. The
default
keyword is useful in Internet service provider and large enterprise
networks where many of the distribution routers have more than 200 interfaces.
Controlling Advertising and Processing in Routing Updates
You can use the
distribute-list
router configuration command with access control lists to suppress routes
from being advertised in routing updates and to prevent other routers from learning one or more routes.
When used in OSPF, this feature applies to only external routes, and you cannot specify an interface
name.
You can also use a
distribute-list
router configuration command to avoid processing certain routes listed
in incoming updates. (This feature does not apply to OSPF.)
Command
Purpose
Step 1
configure terminal
Enter global configuration mode.
Step 2
router
{
bgp
|
rip
|
ospf
|
eigrp
}
Enter router configuration mode.
Step 3
passive-interface
interface-id
Suppress sending routing updates through the specified Layer 3
interface.
Step 4
passive-interface default
(Optional) Set all interfaces as passive by default.
Step 5
no passive-interface
interface type
(Optional) Activate only those interfaces that need to have
adjacencies sent.
Step 6
network
network-address
(Optional) Specify the list of networks for the routing process. The
network-address
is an IP address.
Step 7
end
Return to privileged EXEC mode.
Step 8
copy running-config startup-config
(Optional) Save your entries in the configuration file.
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