3Com Switch 8800 Family Configuration Guide

326 CHAPTER 31: OSPF CONFIGURATION
two ABRs. Both ends of the logic channel should be ABRs and the connection can
take effect only when both ends are configured. The virtual link is identified by the
ID of the remote router. The area, which provides the ends of the virtual link with a
non-backbone area internal route, is called the transit area. The ID of the transit
area should be specified during configuration.
The virtual link is activated after the route passing through the transit area is
calculated, which is equivalent to a p2p connection between two ends. Therefore,
similar to the physical interfaces, you can also configure various interface
parameters on this link, such as hello timer.
The "logic channel" means that the routers running OSPF between two ABRs only
take the role of packet forwarding (the destination addresses of the protocol
packets are not these routers, so these packets are transparent to them and the
routers forward them as common IP packets). The routing information is directly
transmitted between the two ABRs. The routing information herein refers to the
Type-3 LSAs generated by the ABRs, for which the synchronization mode of the
routers in the area will not be changed.
Perform the following configuration in OSPF area view.
By default, the value of hello seconds is 10 seconds, the value of retransmit
seconds is 5 seconds, the value of trans-delay seconds is 1 second, and the value
of dead seconds is 40 seconds.
Configuring Stub Area
of OSPF
Stub areas are some special areas, in which the ABRs do not propagate the learned
external routes of the AS.
The stub area is an optional configuration attribute, but not every area conforms
to the configuration condition. Generally, stub areas, located at the AS
boundaries, are those non-backbone areas with only one ABR. Even if this area has
multiple ABRs, no virtual links are established between these ABRs.
To ensure that the routes to the destinations outside the AS are still reachable, the
ABR in this area will generate a default route (0.0.0.0) and advertise it to the
non-ABR routers in the area.
Pay attention to the following items when configuring a stub area:
■ The backbone area cannot be configured to be the stub area and the virtual
link cannot pass through the stub area.
■ If you want to configure an area to be the stub area, then all the routers in this
area should be configured with this attribute.
Tabl e 298 Configure an OSPF virtual link
Operation Command
Create and configure a
virtual link
vlink-peer router-id [ hello seconds | retransmit seconds |
trans-delay seconds | dead seconds | simple password | md5
keyid key ]*
Remove the created
virtual link
undo vlink-peer router-id