3Com Switch 8800 Configuration Guide
Chapter 19 OSPF Configuration
19-23
Operation
Command
Disable the interface to use MD5
authentication
undo ospf authentication-mode
md5
By default, the interface is not configured with either simple authentication or MD5
authentication.
19.2.20 Configuring OSPF Virtual Link
According to RFC2328, after the area partition of OSPF, not all the areas are equal. In
which, an area is different from all the other areas. Its area-id is 0.0.0.0 and it is usually
called the backbone Area. The OSPF routes between non-backbone areas are
updated with the help of the backbone area. OSPF stipulates that all the non-backbone
areas should maintain the connectivity with the backbone area. That is, at least one
interface on the ABR should fall into the area 0.0.0.0. If an area does not have a direct
physical link with the backbone area 0.0.0.0, a virtual link must be created.
If the physical connectivity cannot be ensured due to the network topology restriction, a
virtual link can satisfy this requirement. The virtual link refers to a logic channel set up
through the area of a non-backbone internal route between 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.
