Categories R&S

OSPF – Building the topology – Configure OSPF virtual link

I’m now configuring OSPF area 10.

Because area 10 is not directly connected to the backbone area, I will need to configure OSPF virtual link.

 

Requirements:

 

Configure OSPF area 10 on R6, R7 and R11.

Advertise R11 loopback 0 prefix.

Configure OSPF virtual link.

 

Diagram:

OSPF - Building the topology - Configure OSPF virtual link

Configuration:

 

I’m enabling the OSPF process and then use the interface level command to configure the three routers.

 

ip ospf 10 area 10
ip ospf network point-to-point

 

At this point, we can see R6 is neighbor with R7 and R11 is neighbor with R7.

 

R7#sh ip ospf neigh

Neighbor ID     Pri   State           Dead Time   Address         Interface
111.111.111.111   0   FULL/  -        00:00:31    10.10.100.2     Ethernet0/1
66.66.66.66       0   FULL/  -        00:00:39    10.10.67.1      Ethernet0/0

But on R7 and R11 are not getting routes from the other devices.

 

R7#sh ip route ospf
      111.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
O        111.11.11.11/32 [110/11] via 10.10.100.2, 00:02:59, Ethernet0/1
O        111.111.111.0/24 [110/11] via 10.10.100.2, 00:02:59, Ethernet0/1

R11#sh ip route ospf
      7.0.0.0/32 is subnetted, 1 subnets
O        7.7.7.7 [110/11] via 10.10.100.1, 00:03:51, Ethernet0/1
      10.0.0.0/8 is variably subnetted, 5 subnets, 2 masks
O        10.10.67.0/30 [110/20] via 10.10.100.1, 00:03:51, Ethernet0/1
      77.0.0.0/24 is subnetted, 1 subnets
O        77.77.77.0 [110/11] via 10.10.100.1, 00:03:51, Ethernet0/1

Let’s configure the virtual link between R6 and R1.

 

R6(config)#router ospf 10
R6(config-router)#area 2 virtual-link 11.11.11.11

R1(config-router)#area 2 virtual-link 66.66.66.66

*Sep  2 09:21:07.283: %OSPF-5-ADJCHG: Process 10, Nbr 11.11.11.11 on OSPF_VL1 from LOADING to FULL, Loading Done
*Sep  2 09:21:07.281: %OSPF-5-ADJCHG: Process 10, Nbr 66.66.66.66 on OSPF_VL1 from LOADING to FULL, Loading Done

Now R11 is getting all the OSPF routes.

 

R11#sh ip route ospf
      7.0.0.0/32 is subnetted, 1 subnets
O        7.7.7.7 [110/11] via 10.10.100.1, 00:03:51, Ethernet0/1
      10.0.0.0/8 is variably subnetted, 5 subnets, 2 masks
O        10.10.67.0/30 [110/20] via 10.10.100.1, 00:03:51, Ethernet0/1
      77.0.0.0/24 is subnetted, 1 subnets
O        77.77.77.0 [110/11] via 10.10.100.1, 00:03:51, Ethernet0/1
R11#sh ip route ospf
      1.0.0.0/32 is subnetted, 1 subnets
O IA     1.1.1.1 [110/41] via 10.10.100.1, 00:01:01, Ethernet0/1
      2.0.0.0/32 is subnetted, 1 subnets
SNIP
O IA     99.99.99.0 [110/61] via 10.10.100.1, 00:01:01, Ethernet0/1
      100.0.0.0/24 is subnetted, 1 subnets
O IA     100.100.100.0 [110/61] via 10.10.100.1, 00:01:01, Ethernet0/1

The show OSPF neigh on R6 and R1 is showing a new adjacency, the interface is listed as “OSPF_VL1” and the network type is “VIRTUAL_LINK”.

 

R6#sh ip ospf neigh
Neighbor ID     Pri   State           Dead Time   Address         Interface
11.11.11.11       0   FULL/  -           -        10.10.14.1      OSPF_VL1

R6#sh ip ospf int
OSPF_VL1 is up, line protocol is up
  Internet Address 10.10.2.6/24, Area 0, Attached via Not Attached
  Process ID 10, Router ID 66.66.66.66, Network Type VIRTUAL_LINK, Cost: 20
  Topology-MTID    Cost    Disabled    Shutdown      Topology Name
        0           20        no                     Base
  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
SNIP
  Neighbor Count is 1, Adjacent neighbor count is 1
    Adjacent with neighbor 11.11.11.11  (Hello suppressed)
  Suppress hello for 1 neighbor(s)

We now have connectivity between OSPF area 10 and the backbone area.

 

Thank you for reading.

 

OSPF – Building the topology – Configure OSPF virtual link