Cisco Systems 3750E manual Changing LSA Group Pacing, Configuring a Loopback Interface, 38-34

Chapter 38 Configuring IP Unicast Routing

Configuring OSPF

Changing LSA Group Pacing

The OSPF LSA group pacing feature allows the router to group OSPF LSAs and pace the refreshing, check-summing, and aging functions for more efficient router use. This feature is enabled by default with a 4-minute default pacing interval, and you will not usually need to modify this parameter. The optimum group pacing interval is inversely proportional to the number of LSAs the router is refreshing, check-summing, and aging. For example, if you have approximately 10,000 LSAs in the database, decreasing the pacing interval would benefit you. If you have a very small database (40 to 100 LSAs), increasing the pacing interval to 10 to 20 minutes might benefit you slightly.

Beginning in privileged EXEC mode, follow these steps to configure OSPF LSA pacing:

	Command	Purpose
Step 1
	configure terminal	Enter global configuration mode.
Step 2
	router ospf process-id	Enable OSPF routing, and enter router configuration mode.
Step 3
	timers lsa-group-pacing seconds	Change the group pacing of LSAs.
Step 4
	end	Return to privileged EXEC mode.
Step 5
	show running-config	Verify your entries.
Step 6
	copy running-config startup-config	(Optional) Save your entries in the configuration file.

To return to the default value, use the no timers lsa-group-pacingrouter configuration command.

Configuring a Loopback Interface

OSPF uses the highest IP address configured on the interfaces as its router ID. If this interface is down or removed, the OSPF process must recalculate a new router ID and resend all its routing information out its interfaces. If a loopback interface is configured with an IP address, OSPF uses this IP address as its router ID, even if other interfaces have higher IP addresses. Because loopback interfaces never fail, this provides greater stability. OSPF automatically prefers a loopback interface over other interfaces, and it chooses the highest IP address among all loopback interfaces.

Beginning in privileged EXEC mode, follow these steps to configure a loopback interface:

	Command	Purpose
Step 1
	configure terminal	Enter global configuration mode.
Step 2
	interface loopback 0	Create a loopback interface, and enter interface configuration mode.
Step 3
	ip address address mask	Assign an IP address to this interface.
Step 4
	end	Return to privileged EXEC mode.
Step 5
	show ip interface	Verify your entries.
Step 6
	copy running-config startup-config	(Optional) Save your entries in the configuration file.

Use the no interface loopback 0 global configuration command to disable the loopback interface.

	Catalyst 3750-E and 3560-E Switch Software Configuration Guide
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