11-3 neighbor ip-address database-filter all out

11-3 neighbor ip-address database-filter all out

Syntax Description:

• ip-address ” IP address of the OSPF neighbor. If a secondary address is used on the interface, then the primary address must be used with this command because OSPF will only form an adjacency using the primary address.

Purpose: To prevent the flooding of link-state advertisements (LSAs) to the indicated neighbor. Many Internet service providers (ISPs) employ redundant links between OSPF neighbors. When an OSPF router receives an LSA, the LSA is flooded on all OSPF inter-faces except for the interface on which the LSA was received. This command allows 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. This command can be used only on a multipoint interface or an NBMA interface.

Initial Cisco IOS Software Release: 12.0

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

In Figure 11-6, there are two parallel links between Routers A and B. To reduce LSA flooding, overhead LSA flooding is prevented on link 2 using the database-filter option of the neighbor command. This reduction of LSA flooding can also be achieved by using the interface command ip ospf database-filter all out (see Section 19-4). Configure Routers A and B as shown in the listing that follows the figure. The point-to-multipoint network type is used on Router A's Serial 0/1 interface and Router B's Serial 0 interface so the database filter can be applied to the interface.

Figure 11-6. Reducing LSA Flooding Overhead by Preventing LSA Flooding on One of the Parallel Links Using the neighbor database-filter all out Command

 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 network point-to-multipoint   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    neighbor 10.1.1.6 database-filter all out   _________________________________________________________________________________________ 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   ip ospf network point-to-multipoint   !   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. The database-filter all out command can be applied only to a point-to-multipoint or NBMA interface.

Step 2. Verify that the OSPF routers have established a FULL adjacency.

Step 3. If the OSPF neighbors have a FULL adjacency, then the command database-filter all out should work.