19-6 ip ospf database-filter all out

19-6 ip ospf database-filter all out

Syntax Description:

This command has no arguments.

Purpose: To prevent the flooding of link-state advertisements (LSAs) on an interface. Many Internet service providers employ redundant links between OSPF neighbors. When an OSPF router receives an LSA, the LSA is flooded on all OSPF interfaces except for the interface on which the LSA was received. The ip ospf database-filter all out command enables an ISP to choose between flooding overhead and flooding reliability. For example, if there are two links between OSPF neighbors, this command can be used to prevent the flooding of LSAs on one of the links.

Initial Cisco IOS Software Release: 12.0

Configuration Example: Reducing the Flooding of LSAs on a Redundant OSPF Link

Figure 19-3 shows two parallel links between Routers A and B. To reduce the LSA flooding overhead, LSA flooding is prevented on link 2 using the database-filter option of the ip ospf interface command. This reduction of LSA flooding can also be achieved by using the router configuration command neighbor ospf database-filter all out (see Section 11-3). Configure Routers A and B as shown in the lines following the figure:

Figure 19-3. LSA Flooding Overhead Can Be Reduced by Preventing LSA Flooding on One of the Parallel Links

 Router A  interface Loopback0   ip address 1.1.1.1 255.255.255.255   !   interface Serial0/0   bandwidth 64   ip address 10.1.1.1 255.255.255.252   !   interface Serial0/1   bandwidth 64   ip address 10.1.1.5 255.255.255.252    ip ospf database-filter all out    clockrate 64000   !   router ospf 1   network 1.1.1.1 0.0.0.0 area 1   network 10.1.1.0 0.0.0.3 area 0   network 10.1.1.4 0.0.0.3 area 0  _________________________________________________________________ Router B  interface Loopback0   ip address 2.2.2.2 255.255.255.255   !   interface Serial0   ip address 10.1.1.6 255.255.255.252   bandwidth 64   !   interface Serial1   bandwidth 64   ip address 10.1.1.2 255.255.255.252   clockrate 64000   !   router ospf 1   network 2.2.2.2 0.0.0.0 area 2   network 10.1.1.0 0.0.0.3 area 0   network 10.1.1.4 0.0.0.3 area 0  

Verification

Verify that the database filter has been applied to interface Serial 0/1 on Router A.

 rtrA#  show ip ospf neighbor detail  Neighbor 2.2.2.2, interface address 10.1.1.2     In the area 0 via interface Serial0/0     Neighbor priority is 1, State is FULL, 6 state changes     DR is 0.0.0.0 BDR is 0.0.0.0     Options 2     Dead timer due in 00:00:33  Neighbor 2.2.2.2, interface address 10.1.1.6     In the area 0 via interface Serial0/1     Neighbor priority is 1, State is FULL, 6 state changes  Database-filter all out  DR is 0.0.0.0 BDR is 0.0.0.0     Options 2     Dead timer due in 00:01:55 

Troubleshooting

Step 1. If the OSPF neighbors have a FULL adjacency , then the interface command ip ospf database-filter all out should work.