Cisco OSPF Command and Configuration Handbook (paperback)

19-8 ip ospf demand-circuit

Syntax Description:

This command has no arguments.

Purpose: On an OSPF demand circuit, periodic Hello messages are suppressed and periodic refreshes of LSAs do not flood the demand circuit. The ip ospf demand-circuit command allows the underlying data link layer to be closed when the topology is stable. In a point-to-multipoint topology, only the multipoint end must be configured with this command. This command is normally used on a tariff link such as ISDN. A tariff link is one that incurs a financial charge for every packet that is sent on the link. Configuring the link as a demand circuit will suppress periodic OSPF packets, reducing the line charges.

Initial Cisco IOS Software Release: 11.2

Configuration Example: Configuring a Point-to-Point Link as an OSPF Demand Circuit

Configure the serial network in Figure 19-5 as an OSPF demand circuit.

Router A interface Loopback0 ip address 1.1.1.1 255.255.255.255 ! interface Serial0/1 ip address 10.1.1.1 255.255.255.252 ip ospf demand-circuit clockrate 64000 ! router ospf 1 network 10.1.1.0 0.0.0.3 area 0 network 1.1.1.1 0.0.0.0 area 1 _________________________________________________________________ Router B interface Loopback0 ip address 2.2.2.2 255.255.255.255 ! interface Serial0 ip address 10.1.1.2 255.255.255.252 ! router ospf 1 network 10.1.1.0 0.0.0.3 area 0 network 2.2.2.2 0.0.0.0 area 2

Verification

Verify that the serial interface has been configured as an OSPF demand circuit.

rtrA# show ip ospf interface serial 0/1 Serial0 is up, line protocol is up Internet Address 10.1.1.1/30, Area 0 Process ID 1, Router ID 1.1.1.1, Network Type POINT_TO_POINT, Cost: 64 Configured as demand circuit. Run as demand circuit. DoNotAge LSA allowed. Transmit Delay is 1 sec, State POINT_TO_POINT, Timer intervals configured, Hello 10, Dead 40, Wait 41, Retransmit 5 Hello due in 00:00:04 Neighbor Count is 1, Adjacent neighbor count is 1 Adjacent with neighbor 2.2.2.2 (Hello suppressed) Suppress hello for 1 neighbor(s)

Verify that the other end of the serial link is configured as a demand circuit even though the command ip ospf demand-circuit was not used on Router B.

rtrB# show ip ospf interface serial 0 Serial0 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 Configured as demand circuit. Run as demand circuit. DoNotAge LSA allowed. Transmit Delay is 1 sec, State POINT_TO_POINT, Timer intervals configured, Hello 10, Dead 40, Wait 41, Retransmit 5 Hello due in 00:00:04 Neighbor Count is 1, Adjacent neighbor count is 1 Adjacent with neighbor 1.1.1.1 (Hello suppressed) Suppress hello for 1 neighbor(s)

Verify that Routers A and B have established an OSPF neighbor relationship.

rtrA# show ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface 2.2.2.2 1 FULL/ - 00:00:35 10.1.1.2 Serial0/1

Troubleshooting

Step 1. The ip ospf demand-circuit command will work if there are no errors in the configuration. Before using this command, ensure that the routers have established an OSPF neighbor relationship over the link that is to be configured as a demand circuit.