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Catalyst 3750-E and 3560-E Switch Software Configuration Guide
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Chapter38 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 usual ly need to modify this parameter. The
optimum group pacing interval is inversely proportional to the number of LSAs the router is refreshi ng,
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 databa se (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:
To return to the default value, use the no timers lsa-group-pacing router 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. Becau se 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:
Use the no interface loopback 0 global configuration command to disable t he loopback interface.
Command Purpose
Step1 configure terminal Enter global configuration mode.
Step2 router ospf process-id Enable OSPF routing, and enter router configuration mode.
Step3 timers lsa-group-pacing seconds Change the group pacing of LSAs.
Step4 end Return to privileged EXEC mode.
Step5 show running-config Verify your entries.
Step6 copy running-config startup-config (Optional) Save your entries in the configuration file.
Command Purpose
Step1 configure terminal Enter global configuration mode.
Step2 interface loopback 0 Create a loopback interface, and enter interface configuration mode.
Step3 ip address address mask Assign an IP address to this interface.
Step4 end Return to privileged EXEC mode.
Step5 show ip interface Verify your entries.
Step6 copy running-config startup-config (Optional) Save your entries in the configuration file.