A company is using OSPF between its HQ location and a branch office.

OSPF requires all nonbackbone areas to connect logically to Area 0. In the original design, HQ is Area 0 and the existing branch is Area 1, which is valid because Area 1 has connectivity to the backbone. The newly acquired branch is assigned Area 2 but is temporarily connected through the existing branch instead of directly to HQ. That means Area 2 does not have a direct logical connection to Area 0, violating the OSPF backbone requirement. The proper OSPF design mechanism for this temporary topology is a virtual link. An OSPF virtual link is configured through a transit area to logically connect a disconnected area or ABR back to the backbone. Making the existing branch a stub area does not solve the lack of Area 0 connectivity. A sham link is used in MPLS VPN OSPF designs to prefer backdoor links or preserve intra-area behavior across the provider core, not for this generic backbone disconnection. Making Area 2 a stub area also does not establish backbone reachability. Therefore, a virtual link between the new branch and HQ is required.