HP 6125G Configuration Manual page 61

Figure 14 Virtual link application 1
Virtual links can also be used to provide redundant links. If the backbone area cannot maintain internal
connectivity due to the failure of a physical link, you can configure a virtual link to replace the failed
physical link, as shown in
Figure 15 Virtual link application 2
R1
The virtual link between the two ABRs acts as a point-to-point connection. You can configure interface
parameters such as hello interval on the virtual link as they are configured on a physical interface.
The two ABRs on the virtual link unicast OSPF packets to each other, and the OSPF routers in between
convey these OSPF packets as normal IP packets.
Stub area
A stub area does not distribute Type-5 LSAs, so the routing table size and amount of routing information
in this area are reduced significantly. The ABR generates a default route into the area.
You can configure the stub area as a totally stub area, where the ABR advertises neither inter-area routes
nor external routes.
Stub area configuration is optional, and not every area is eligible to be a stub area. In general, a stub
area resides on the border of the AS.
When you configure a totally stub area, follow these guidelines:
The backbone area cannot be a totally stub area.
•
To configure an area as a stub area, the stub command must be configured on routers in the area.
•
• To configure an area as a totally stub area, the stub command must be configured on routers in the
area, and the ABR of the area must be configured with the stub [ no-summary ] command.
A totally stub area cannot have an ASBR because AS external routes cannot be distributed into the
•
stub area.
Virtual links cannot transit totally stub areas.
•
Figure 15.
Area 1
Virtual link
R2
Area 0
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