13-2 passive-interface default

Syntax Description:

This form of the command has no arguments.

Purpose: To make all OSPF interfaces passive.

Initial Cisco IOS Software Release: 12.0

Configuration Example: Many Interfaces, Few Neighbors

In Figure 13-2, Router A has one OSPF neighbor and connections to five non-OSPF routers. Router A wants to advertise all connected networks to Router B via OSPF, but does not want to transmit OSPF traffic on the interfaces connecting to non-OSPF routers. In addition, Router A wants to advertise the connected networks as OSPF routes. This condition means that redistributing connected routes on Router A is not an option, because these routes would be advertised as external routes.

Figure 13-2. All OSPF Interfaces Can Be Made Passive Using the Command passive-interface default. The no Form of the Command Can Then Be Used to Enable Selected Interfaces

For the moment, assume that the default option is not available with the passive-interface command. The configuration for Router A would require five passive-interface commands.

 Router A  router ospf 1   passive-interface Serial1/0   passive-interface Serial1/1   passive-interface Serial1/2   passive-interface Serial1/3   passive-interface Serial1/4   network 10.1.0.0 0.0.255.255 area 0  

The OSPF configuration for Router A is not very complicated. But assume that you have a core router with over 100 interfaces to non-OSPF routers. The configuration would become rather cumbersome. There would be over 100 passive-interface statements in the OSPF configuration. Therefore, the default option is an option of convenience. Start by using the command passive-interface default to make all OSPF interfaces passive. Then activate the interfaces that have OSPF neighbors, using the no passive-interface form of the command. The previous configuration would become

  router ospf 1    passive-interface default    no passive-interface Serial0/1   network 10.1.0.0 0.0.255.255 area 0  

Verification

Verify that the Serial 1 interface is a passive OSPF interface.

 rtrB#  show ip ospf interface  Loopback0 is up, line protocol is up   Internet Address 2.2.2.2/32, Area 2   Process ID 1, Router ID 2.2.2.2, Network Type LOOPBACK, Cost: 1   Loopback interface is treated as a stub Host Serial0/1 is up, line protocol is up   Internet Address 10.1.1.2/30, Area 0   Process ID 1, Router ID 2.2.2.2, Network Type POINT_TO_POINT, Cost: 64   Transmit Delay is 1 sec, State POINT_TO_POINT,   Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5     Hello due in 00:00:02   Neighbor Count is 1, Adjacent neighbor count is 1     Adjacent with neighbor 1.1.1.1   Suppress hello for 0 neighbor(s) Serial1/0 is up, line protocol is up   Internet Address 10.1.1.5/30, Area 0   Process ID 1, Router ID 2.2.2.2, Network Type POINT_TO_POINT, Cost: 1562   Transmit Delay is 1 sec, State POINT_TO_POINT,   Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5  No Hellos (Passive interface)  Neighbor Count is 0, Adjacent neighbor count is 0   Suppress hello for 0 neighbor(s) ... 

Troubleshooting

Step 1. When using the default option, make sure that interfaces with OSPF neighbors have been made active using the no passive-interface command.