LAB: OSPF demand Circuit

OSPF to support Demand circuits, in which OSPF Hellos and the refresh of OSPF routing information are suppressed on demand circuits.  This allows the underlying data-link connections to be closed when not carrying application traffic.  This is useful for low-speed and pay as you use links like in ISDN circuits.


interface command

ip ospf demand-circuit

Verification before applying the command;

Rack1R4#sho ip ospf interface  s0/1
Serial0/1 is up, line protocol is up
  Internet Address 155.1.45.4/24, Area 0
  Process ID 1, Router ID 223.255.255.255, Network Type POINT_TO_POINT, Cost: 1
  Enabled by interface config, including secondary ip addresses
  Transmit Delay is 1 sec, State POINT_TO_POINT,
  Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
    oob-resync timeout 40
    Hello due in 00:00:05
  Supports Link-local Signaling (LLS)
  Index 3/4, flood queue length 0
  Next 0x0(0)/0x0(0)
  Last flood scan length is 1, maximum is 1
  Last flood scan time is 4 msec, maximum is 4 msec
  Neighbor Count is 1, Adjacent neighbor count is 1
    Adjacent with neighbor 150.1.5.5
  Suppress hello for 0 neighbor(s)

Rack1R4#sho ip ospf neighbor

Neighbor ID     Pri   State           Dead Time   Address         Interface
150.1.5.5         0   FULL/  -        00:00:34    155.1.45.5      Serial0/1
150.1.5.5         0   FULL/  -        00:01:52    155.1.0.5       Serial0/0
150.1.1.1         1   FULL/BDR        00:00:36    155.1.146.1     FastEthernet0/1
150.1.6.6       255   FULL/DR         00:00:32    155.1.146.6     FastEthernet0/1

as you can see the output above, there is 0 neighbors with suppress hellos.  in this case we will activate the demand circuit for s0/1 interface.

Rack1R4(config)#int s0/1
Rack1R4(config-if)#ip ospf demand-circuit


verification:

Rack1R4#show ip ospf interface s0/1
Serial0/1 is up, line protocol is up
  Internet Address 155.1.45.4/24, Area 0
  Process ID 1, Router ID 223.255.255.255, Network Type POINT_TO_POINT, Cost: 1
  Enabled by interface config, including secondary ip addresses
  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 40, Retransmit 5
    oob-resync timeout 40
    Hello due in 00:00:01
  Supports Link-local Signaling (LLS)
  Index 3/4, flood queue length 0
  Next 0x0(0)/0x0(0)
  Last flood scan length is 1, maximum is 1
  Last flood scan time is 4 msec, maximum is 4 msec
  Neighbor Count is 1, Adjacent neighbor count is 1
    Adjacent with neighbor 150.1.5.5  (Hello suppressed)
  Suppress hello for 1 neighbor(s)

Rack1R4#show ip ospf neighbor

Neighbor ID     Pri   State           Dead Time   Address         Interface
150.1.5.5         0   FULL/  -           -        155.1.45.5      Serial0/1
150.1.5.5         0   FULL/  -        00:01:44    155.1.0.5       Serial0/0
150.1.1.1         1   FULL/BDR        00:00:38    155.1.146.1     FastEthernet0/1
150.1.6.6       255   FULL/DR         00:00:34    155.1.146.6     FastEthernet0/1

the output above shows that there is 1 neighbor in s0/1 interface with Hellos being supressed, this further validates by the "show ip ospf neighbor" output indicating the neighbor via s0/1 having a no Dead time.