Cisco Systems 78-11741-02 Reducing LSA Flooding, Ignoring Mospf LSA Packets, Mospf LSA packets

Configuring OSPF

Reducing LSA Flooding

Command	Purpose
Router(config-if)#ospf database-filter all	Blocks the flooding of OSPF LSA packets to the interface.
out

On point-to-multipoint networks, to prevent flooding of OSPF LSAs, use the following command in router configuration mode:

Command	Purpose
Router(config-router)# neighbor ip-address	Blocks the flooding of OSPF LSA packets to the specified neighbor.
database-filter all out

For an example of blocking LSA flooding, see the section “Block LSA Flooding Example” at the end of this chapter.

Reducing LSA Flooding

The explosive growth of the Internet has placed the focus on the scalability of IGPs such as OSPF. By design, OSPF requires LSAs to be refreshed as they expire after 3600 seconds. Some implementations have tried to improve the flooding by reducing the frequency to refresh from 30 minutes to about 50 minutes. This solution reduces the amount of refresh traffic but requires at least one refresh before the LSA expires. The OSPF flooding reduction solution works by reducing unnecessary refreshing and flooding of already known and unchanged information. To achieve this reduction, the LSAs are now flooded with the higher bit set. The LSAs are now set as “do not age.”

To reduce unnecessary refreshing and flooding of LSAs on your network, use the following command in interface configuration mode:

Command	Purpose
Router(config-if)#ip ospf flood-reduction	Suppresses the unnecessary flooding of LSAs in stable topologies.

Ignoring MOSPF LSA Packets

Cisco routers do not support LSA type 6 Multicast OSPF (MOSPF), and they generate syslog messages if they receive such packets. If the router is receiving many MOSPF packets, you might want to configure the router to ignore the packets and thus prevent a large number of syslog messages. To do so, use the following command in router configuration mode:

Command	Purpose
Router(config-router)# ignore lsa mospf	Prevents the router from generating syslog messages when it receives
	MOSPF LSA packets.

For an example of suppressing MOSPF LSA packets, see the section “Ignore MOSPF LSA Packets Example” at the end of this chapter.

Cisco IOS IP Configuration Guide

IPC-238