Configuring a virtual link

For information about virtual links, see Configuring an ABR to use a virtual link to the backbone.

Syntax:

ip ospf area area-id virtual linkip-address

Used on a pair of ABRs at opposite ends of a virtual link in the same area to configure the virtual link connection.

area-id

This must be the same for both ABRs in the link and is the area number of the virtual link transit area in either decimal or dotted decimal format.

ip-address

On an ABR directly connected to the backbone area, this value must be the IP address of an ABR (in the same area) needing a virtual link to the backbone area as a substitute for a direct physical connection.

On the ABR that needs the virtual link to the backbone area, this value must be the IP address of the ABR (in the same area) having a direct physical connection to the backbone area.

Example

Figure 37: Defining OSPF virtual links within a network shows an OSPF ABR, routing switch "A" that lacks a direct connection to the backbone area (area 0.) To provide backbone access to routing switch "A," you can add a virtual link between routing switch "A" and routing switch "C," using area 1 as a transit area.

To configure the virtual link, define it on the routers that are at each end of the link. No configuration for the virtual link is required on the other routers on the path through the transit area (such as routing switch "B" in this example.)

Figure 37: Defining OSPF virtual links within a network

switch(ospf)# area 1 virtual-link 209.157.22.1

switch(ospf)# area 1 virtual-link 10.0.0.1

For descriptions of virtual link interface parameters you can either use in their default settings or reconfigure as needed, see Changing the dead interval on a virtual link.