What is the purpose of an Open Shortest Path First (OSPF) virtual link?

The purpose of an Open Shortest Path First (OSPF) virtual link is to connect area border routers over a non-backbone area. In OSPF, the backbone area (Area 0) is essential for the proper operation of the protocol, as it serves as the central hub for communication between different OSPF areas. When there is a need to connect two area border routers that are not directly connected through the backbone, a virtual link is established.

This virtual link allows the non-backbone area to effectively communicate with the backbone area, facilitating route exchanges and maintaining OSPF area integrity. The use of a virtual link ensures that OSPF can maintain optimal routing without requiring all routers to be directly connected to Area 0. Thus, it plays a crucial role in OSPF's capability to scale by allowing areas to be connected indirectly while adhering to the OSPF design principles.