Example for Configuring OSPF Virtual Links

This section describes how to configure virtual links to connect a non-backbone area to the backbone area.

Networking Requirements

On the network shown in Figure 1, Area 2 is not directly connected to the backbone area Area 0. Area 1 serves as a transit area to connect Area 2 and Area 0. A virtual link is configured between Device A and Device B.

Figure 1 Networking for configuring an OSPF virtual links

Interfaces 1 and 2 in this example represent GE 0/1/0 and GE 0/1/8, respectively.

Precautions

The default value is recommended when a virtual link is created. You can modify the value in actual scenarios.

Suggestions for configuring parameters are as follows:

The smaller the hello parameter, the more rapidly a router detects network topology change, the more network resources are consumed.
If the retransmit parameter is set too small, LSAs may be retransmitted. Setting the parameter to a large value is recommended in a low-speed network.
The authentication modes of a virtual link and the backbone area must be the same.

Configuration Roadmap

The configuration roadmap is as follows:

Configure basic OSPF functions on each router.
Configure a virtual link between Device A and Device B to connect a non-backbone area to the backbone area.

Data Preparation

To complete the configuration, you need the following data:

Device Name	Router ID	Process ID	IP Address
Device A	1.1.1.1	1	Area 0: 10.0.0.0/8 Area 1: 192.168.1.0/24
Device B	2.2.2.2	1	Area 1: 192.168.1.0/24 Area 2: 172.16.0.0/16
Device C	3.3.3.3	1	Area 0: 10.0.0.0/8
Device D	4.4.4.4	1	Area 2: 172.16.0.0/16

Procedure

Assign an IP address to each interface. For configuration details, see Configuration Files in this section.
Configure basic OSPF functions.
For configuration details, see Configuring Basic OSPF Functions.

Check the OSPF routes on Device A

[~DeviceA] display ospf routing
          OSPF Process 1 with Router ID 1.1.1.1

                   Routing Tables

 Routing for Network
 Destination        Cost       Type       NextHop         AdvRouter       Area
 10.0.0.0/8         1          Transit    10.1.1.1        3.3.3.3         0.0.0.0
 192.168.1.0/24     1          Transit    192.168.1.1     1.1.1.1         0.0.0.1

 Total Nets: 2
 Intra Area: 2  Inter Area: 0  ASE: 0  NSSA: 0

The routing table on Device A contains no route in Area 2 because Area 2 is not directly connected to Area 0.

Configure an OSPF virtual link.

# Configure Device A.

[~DeviceA] router id 1.1.1.1
[~DeviceA] ospf 1
[*DeviceA-ospf-1] area 1
[*DeviceA-ospf-1-area-0.0.0.1] vlink-peer 2.2.2.2
[*DeviceA-ospf-1-area-0.0.0.1] quit
[*DeviceA-ospf-1] quit
[*DeviceA] commit

# Configure Device B.

[~DeviceB] router id 2.2.2.2
[~DeviceB] ospf 1
[*DeviceB-ospf-1] area 1
[*DeviceB-ospf-1-area-0.0.0.1] vlink-peer 1.1.1.1
[*DeviceB-ospf-1-area-0.0.0.1] quit
[*DeviceB-ospf-1] quit
[*DeviceB] commit

Verify the configuration.

# Display the OSPF vlink on Device A.

[~DeviceA] display ospf vlink
          OSPF Process 1 with Router ID 1.1.1.1
                  Virtual Links
 Virtual-link Neighbor-id  -> 2.2.2.2, Neighbor-State: Full
 Interface: 192.168.1.1 (GigabitEthernet0/1/0)
 Cost: 1  State: P-2-P  Type: Virtual
 Transit Area: 0.0.0.1
 Timers: Hello 10 , Dead 40 , Retransmit 5 , Transmit Delay 1
 GR State: Normal

The preceding command output shows that the OSPF vlink neighbor status is "Full".

# Display the OSPF routes on Device A.

[~DeviceA] display ospf routing
          OSPF Process 1 with Router ID 1.1.1.1

                   Routing Tables

 Routing for Network
 Destination        Cost       Type       NextHop         AdvRouter       Area
 172.16.0.0/16      2          Inter-area 192.168.1.2     2.2.2.2         0.0.0.2
 10.0.0.0/8         1          Transit    10.1.1.1        1.1.1.1         0.0.0.0
 192.168.1.0/24     1          Transit    192.168.1.1     1.1.1.1         0.0.0.1

 Total Nets: 3
 Intra Area: 2  Inter Area: 1  ASE: 0  NSSA: 0

After the virtual link is configured, the routing table on Device A contains routes in Area 2.

Configuration Files

Device A configuration file

#
sysname DeviceA
#
router-id 1.1.1.1
#
interface GigabitEthernet0/1/0
 undo shutdown
 ip address 192.168.1.1 255.255.255.0
#
interface GigabitEthernet0/1/8
 undo shutdown
 ip address 10.1.1.1 255.0.0.0
#
ospf 1
 area 0.0.0.0
  network 10.0.0.0 0.255.255.255
 area 0.0.0.1
  network 192.168.1.0 0.0.0.255
  vlink-peer 2.2.2.2
#
return

Device B configuration file

#
sysname DeviceB
#
router-id 2.2.2.2
#
interface GigabitEthernet0/1/0
 undo shutdown
 ip address 192.168.1.2 255.255.255.0
#
interface GigabitEthernet0/1/8
 undo shutdown
 ip address 172.16.1.1 255.255.0.0
#
ospf 1
 area 0.0.0.1
  network 192.168.1.0 0.0.0.255
  vlink-peer 1.1.1.1
 area 0.0.0.2
  network 172.16.0.0 0.0.255.255
#
return

Device C configuration file

#
sysname DeviceC
#
router-id 3.3.3.3
#
interface GigabitEthernet0/1/8
 undo shutdown
 ip address 10.1.1.2 255.0.0.0
#
ospf 1
 area 0.0.0.0
  network 10.0.0.0 0.255.255.255
#
return

Device D configuration file

#
sysname DeviceD
#
router-id 4.4.4.4
#
interface GigabitEthernet0/1/8
 undo shutdown
 ip address 172.16.1.2 255.255.0.0
#
ospf 1
 area 0.0.0.2
  network 172.16.0.0 0.0.255.255
#
return