LAB: OSPF Virtual Link

OSPF Virtual Link allows the forming of an indirect area 0 adjacency, which can be used to repair breaks in the OSPF domain or solve traffic engineering requirements.

in this diagram area 2 has 2 exits to reach area 0 one thru R3 2nd is thru R6, in case R3 link is down, Area 2 will be disconnected from Area 0. in this case R6 can virtual-link to neighbor R1 or R4 in Area 1.

neighbors forming the adjacency over the virtual-link dont have to be directly connected.

commands:

Rack1R1(config)#router ospf 1
Rack1R1(config-router)#area 1 virtual-link 150.1.6.6


Rack1R6(config)#router ospf 1
Rack1R6(config-router)#area 1 virtual-link 150.1.1.1

verification:

Rack1R6#show ip ospf interface
OSPF_VL0 is up, line protocol is up
Internet Address 155.1.146.6/24, Area 0
Process ID 1, Router ID 150.1.6.6, Network Type VIRTUAL_LINK, Cost: 300
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 00:00:03
Supports Link-local Signaling (LLS)
Index 1/4, 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 150.1.1.1 (Hello suppressed)
Suppress hello for 1 neighbor(s)
FastEthernet0/0.146 is up, line protocol is up
Internet Address 155.1.146.6/24, Area 1
Process ID 1, Router ID 150.1.6.6, Network Type BROADCAST, Cost: 300
Enabled by interface config, including secondary ip addresses
Transmit Delay is 1 sec, State DR, Priority 255


Rack1R6#sho ip ospf neighbor

Neighbor ID Pri State Dead Time Address Interface
150.1.1.1 0 FULL/ - - 155.1.146.1 OSPF_VL0
150.1.1.1 1 FULL/BDR 00:00:36 155.1.146.1 FastEthernet0/0.146
223.255.255.255 0 FULL/DROTHER 00:00:34 155.1.146.4 FastEthernet0/0.146
150.1.7.7 1 FULL/BDR 00:00:30 155.1.67.7 FastEthernet0/0.67
Rack1R6#