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OUTING
3-321
Configuring Virtual Links
All OSPF areas must
connect to the backbone. If
an area does not have a
direct physical connection to
the backbone, you can
configure a virtual link that
provides a logical path to the
backbone. To connect an
isolated area to the
backbone, the logical path
can cross a single
non-backbone area (i.e.,
transit area) to reach the backbone. To define this path, you must configure
an ABR that serves as an endpoint connecting the isolated area to the
common transit area, and specify a neighboring ABR as the other endpoint
connecting the common transit area to the backbone itself. (Note that you
cannot configure a virtual link that runs through a stub or NSSA area.)
Virtual links can also be used to create a redundant link between any area
and the backbone to help prevent partitioning, or to connect two existing
backbone areas into a common backbone.
Command Attributes
• Area ID – Identifies the transit area for the virtual link.
(The area ID must be in the form of an IP address.)
• Neighbor Router ID – Neighbor router at other end of the virtual link.
This must be an Area Border Router (ABR) that is adjacent to both the
backbone and the transit area for the virtual link.
• Events – The number of state changes or error events on this virtual
link.
The other items are described under “Configuring OSPF Interfaces,”
page 3-315.
Note: This router supports up 64 virtual links.
backbone
normal
area
isolated
area
ABR
ABR
virtual
link