Operation Manual – IPv4 Routing
H3C S3610&S5510 Series Ethernet Switches
Chapter 3 OSPF Configuration
3-6
Figure 3-2
OSPF router types
III. Backbone area and virtual links
Each AS has a backbone area, which is responsible for distributing routing information
between none-backbone areas. Routing information between non-backbone areas
must be forwarded by the backbone area. Therefore, OSPF requires that:
z
All non-backbone areas must maintain connectivity to the backbone area.
z
The backbone area itself must maintain connectivity.
In practice, due to physical limitations, the requirements may not be satisfied. In this
case, configuring OSPF virtual links is a solution.
A virtual link is established between two area border routers via a non-backbone area
and is configured on both ABRs to take effect. The area that provides the
non-backbone area internal route for the virtual link is a “transit area”.
In the following figure, Area 2 has no direct physical link to the backbone area 0.
Configuring a virtual link between ABRs can connect Area 2 to the backbone area.
Figure 3-3
Virtual link application 1
