System information

BSR 64000 Configuration and Management Guide
11-22
Blocking OSPF LSA Flooding
The OSPF LSA age indicates whether the LSA is valid. The LSA is discarded when it
reaches the maximum age of one hour. During the aging process, the originating
router sends a refresh packet every 30 minutes to keep the LSA from expiring,
regardless of network topology changes. The router tracks and refreshes the LSAs it
generates; it tracks and ages the LSAs it receives from other routers. Each LSA is
refreshed when it is 30 minutes old, independent of other LSAs.
By default, OSPF floods new LSAs over all interfaces in the same area, except the
interface on which the LSA arrives. Some redundancy is desirable, because it ensures
robust flooding. However, too much redundancy can waste bandwidth and might
destabilize the network due to excessive link and CPU usage in certain topologies.
To block the flooding of OSPF LSAs on broadcast, non-broadcast, and point-to-point
networks, use the ip ospf database-filter all out command in Interface Configuration
mode, as shown below:
MOT(config-if)#ip ospf database-filter all out
Examples
The following example prevents flooding of OSPF LSAs to broadcast, non-broadcast,
or point-to-point networks accessible through Ethernet interface 7/0:
interface ethernet 7/0
ip ospf database-filter all out
Configuring a Passive Interface for OSPF
To prevent OSPF from flooding an interface, you can configure the interface as a
passive network. This prevents OSPF from sending hello packets for that interface.
Both devices are able to see each other via the hello packet generated for the receiving
interface.
You can configure a passive interface to prevent other routers on a local network from
learning about routes dynamically. A passive interface does not transmit routing
updates.
Use the passive-interface command in Router Configuration mode to create a passive
OSPF interface, as shown in the following example: