ip ospf database-filter all out

From: "Brian McGahan" <brian@xxxxxxxxxxxxxxx> To: "'Robert Massiache'" <robert2140@xxxxxxxxxxx>, <ccielab@xxxxxxxxxxxxxx> Subject: RE: No LSA Command Date: Sun, 20 Oct 2002 10:27:40 -0500 Robert, The command "ip ospf database-filter all out" works like passive interface does in distance vector protocols. When you say 'passive interface' in OSPF, you deny sending any hello packets out an interface, therefore an adjacency cannot be established. With 'ip ospf database-filter' on the other hand, you are only filtering the LSA generation. This means that you can still establish adjacencies (since hellos are still sent), but you won't send your neighboring router any LSA's. Therefore you will receive all the LSA's in their database, but they will not receive any of yours. Observe the following: R1--12.0.0.0/8--R2 R1 and R2 share an Ethernet segment running OSPF. They each advertise a prefix into the OSPF domain, 1.1.1.1/32 and 2.2.2.2/32 respectively. R2 uses the command 'ip ospf database-filter all out' on the Ethernet segment between them. Therefore, R1 does not receive the LSA 2.2.2.2/32 in its OSPF database (and therefore the IP routing table), yet R2 still does receive the LSA 1.1.1.1/32 and installs it in the IP routing table. R1#sh ip int brief Interface IP-Address OK? Method Status Protocol FastEthernet0/0 12.0.0.1 YES manual up up Loopback0 1.1.1.1 YES manual up up ! R1#sh run | b router ospf router ospf 1 network 0.0.0.0 255.255.255.255 area 0 ! R1#sh ip ospf nei Neighbor ID Pri State Dead Time Address Interface 2.2.2.2 1 FULL/DR 00:00:35 12.0.0.2 FastEthernet0/0 ! R2#sh ip int brief Interface IP-Address OK? Method Status Protocol Ethernet0 12.0.0.2 YES manual up up Loopback0 2.2.2.2 YES manual up up ! R2#sh run int e0 interface Ethernet0 ip address 12.0.0.2 255.0.0.0 ip ospf database-filter all out end ! R2#sh run | b router ospf router ospf 1 network 0.0.0.0 255.255.255.255 area 0 ! R2#sh ip ospf nei Neighbor ID Pri State Dead Time Address Interface 1.1.1.1 1 FULL/BDR 00:00:37 12.0.0.1 Ethernet0 ! R2#sh ip route <snip> 1.0.0.0/32 is subnetted, 1 subnets O 1.1.1.1 [110/11] via 12.0.0.1, 00:05:43, Ethernet0 2.0.0.0/32 is subnetted, 1 subnets C 2.2.2.2 is directly connected, Loopback0 C 12.0.0.0/8 is directly connected, Ethernet0 ! R1#sh ip route <snip> 1.0.0.0/32 is subnetted, 1 subnets C 1.1.1.1 is directly connected, Loopback0 C 12.0.0.0/8 is directly connected, FastEthernet0/0 R1# ! R1#sh ip ospf dat OSPF Router with ID (1.1.1.1) (Process ID 1) Router Link States (Area 0) Link ID ADV Router Age Seq# Checksum Link count 1.1.1.1 1.1.1.1 475 0x80000005 0x7B7B 2 ! R2#sh ip ospf dat OSPF Router with ID (2.2.2.2) (Process ID 1) Link ID ADV Router Age Seq# Checksum Link count 1.1.1.1 1.1.1.1 480 0x80000005 0x7B7B 2 2.2.2.2 2.2.2.2 486 0x80000006 0x27B8 2 Net Link States (Area 0) Link ID ADV Router Age Seq# Checksum 12.0.0.2 2.2.2.2 488 0x80000001 0x29EE ! HTH Brian McGahan, CCIE #8593 Director of Design and Implementation brian@xxxxxxxxxxxxxxx CyscoExpert Corporation Internetwork Consulting & Training Voice: 847.674.3392 Fax: [phone]

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