126 CHAPTER 15: ROUTING CONFIGURATION GUIDE
Configuring OSPF
Virtual Link
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.
Network Diagram
Figure 34 Networking diagram for OSPF virtual link
Networking and
Configuration
Requirements
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.
Applicable Products
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 BSwitch A
Vlan-int1
Area 1
Virtual link
Area 2
Vlan-int2
Vlan-int1
Product series Software version Hardware version
Switch 5500 Release V03.02.04 All versions
Switch 5500G Release V03.02.04 All versions
Switch 4500 Release V03.03.00 All versions
