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Catalyst 3750-E and 3560-E Switch Software Configuration Guide
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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:
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. 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:
Use the no interface loopback 0 global configuration command to disable the loopback interface.
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.
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.
