3com 4200G ユーザーズマニュアル

C

HAPTER

 15: R

OUTING

 C

ONFIGURATION

 G

UIDE

Among OSPF areas in an AS, one area is different from any other area. Its area ID is 
0 and it is usually called the backbone area. The backbone area is responsible for 
distributing routing information between none-backbone areas. Therefore, OSPF 
requires that:

■

All non-backbone areas must maintain connectivity to the backbone area.

■

The backbone area must maintain connectivity within itself.

In practice, the requirements may not be satisfied due to physical limitations. In 
this case, configuring OSPF virtual links is a solution.

A virtual link is established between two ABRs through a non-backbone area and 
is configured on both ABRs to take effect. The non-backbone area is a transit area.

Figure 34   Networking diagram for OSPF virtual link

Configure OSPF in the network, which is divided into three areas: the backbone 
area and two non-backbone areas (Area 1 and Area 2). Area 2 has no direct 
connection to the backbone area; the connection from Area 2 to the backbone 
area must go through Area 1. The user hopes to enable Area 2 to communicate 
with the other two areas.

Based on the user requirements and network environment, configure a virtual link 
to connect Area 2 to the backbone area.

Device Interface 

IP 

address 

Router 

ID 

Switch A 

Vlan-int1 

196.1.1.2/24 1.1.1.1 

Vlan-int2 197.1.1.2/24 

- 

Switch B 

Vlan-int1 

152.1.1.1/24 2.2.2.2 

Vlan-int2 197.1.1.1/24 

-

Area 0

Switch B

Switch A

Vlan-int1

Area 1

Virtual link

Area 2

Vlan-int2

Vlan-int1

Switch 5500

Release V03.02.04 

All versions 

Switch 5500G

Release V03.02.04 

All versions 

Switch 4500

Release V03.03.00 

All versions