The single backbone area (area 0.0.0.0) cannot be disconnected, or certain areas of the Autonomous System will become unreachable. To establish and maintain connectivity of the backbone, virtual links can be configured through non-backbone areas. Virtual links serve to connect physically separate components of the backbone.
set protocols ospf4 vrf <vrf-name> area <area-id1> virtual-link <router-id> transmit-area <area-id2>
•<vrf-name> Optional. Specifies a VRF name. The value is a string. It’s a user-defined VRF set by the command set ip vrf <vrf-name> [description <string>].
Note that: The configuration is in the default VRF if not explicitly bound to any VRF.
•<area-id1> The OSPF area to which the attached network belongs.
• <router-id> A unique 32-bit identifier within this AS.
• <area-id2> Area through which to transmit.
This example configure the virtual link on the Area Border Router switch B(18.104.22.168) and Switch C(22.214.171.124), After this step, there will be a route entry from the backbone area, 0.0.0.0, to area 126.96.36.199.