3Com 3032 Configuration Manual page 439

The virtual link is activated after the route through the transit area is calculated. It
is equivalent to a point-to-point connection between two terminals. Parameters
can be configured for this connection like a physical interface, such as sending a
hello-timer.
A "logic channel" is provided for multiple routers running OSPF that forwards
messages between two ABRs. Since the destination addresses of the protocol
messages are not these ABRs, the messages are transparent to them and they are
transmitted as ordinary IP messages, while routing information is transmitted
directly between the two ABRs. Routing information here means an LSA of Type3
that is generated by ABR. The synchronization of routers in the area is not
changed.
When configuring a backbone area, note that:
The backbone area is responsible for advertising the routing information of the
non-backbone area. If the AS is divided into more than one area, one area
must be the backbone area, and other areas must be connected with the
backbone area directly or logically.
The backbone area must include all ABRs, and may include routers belonging
to the backbone area only. An ASBR may not be inside the backbone area.
ABRs inside the backbone area must be well connected, and may be connected
physically or logically (establishing virtual connection between ABRs).
When configuring a virtual connection, note that:
A virtual connection can only span one area, which means that the
non-backbone area can establish virtual connection with the backbone area
only by spanning one other non-backbone area.
Multiple virtual connections can be connected in series to form a new virtual
connection.
Perform the following configurations in OSPF view.
Table 501 Create and Configuring a Virtual Link
Operation
Create and configure a virtual link
Delete the specified virtual link
By default, there is no virtual link is created. The attributes for this command have
the following default values:
: None
area-id
: None
router-id
10 seconds
hello-timer:
retransmit-timer:
: 1 second
transit-delay
Command
vlink peer-id router-id transit-area
area-id [ hello-timer seconds ] [
retransmit-timer seconds ] [
transit-delay seconds ] [ dead-timer
seconds ]
undo vlink peer-id router-id
transit-area area-id
5 seconds
Configuring OSPF 435