Microsoft ES4649 IP Routing Configuring Virtual Links, To reach the backbone. To define this

IP Routing 3

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				isolated
				area
virtual link that provides a logical
path to the backbone. To connect an
isolated area to the backbone, the				ABR
logical path can cross a single
non-backbone area (i.e., transit area)			virtual
to reach the backbone. To define this			link
path, you must configure an ABR	backbone	ABR		normal
that serves as an endpoint
				area
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 3-243.

Note: This router supports up 64 virtual links.

3-247