What is the primary function of an Open Shortest Path First (OSPF) area border router (ABR)?

The primary function of an Open Shortest Path First (OSPF) area border router (ABR) centers on maintaining a link-state database. An ABR serves as a boundary between different OSPF areas and facilitates the exchange of routing information between these areas. By maintaining a link-state database, the ABR ensures that it has a comprehensive view of the network topology within its own area, while also correctly summarizing and propagating necessary routing information between adjacent areas.

This function is critical for OSPF's efficiency and operational effectiveness, as it allows for optimal route calculation using advanced methods such as the Dijkstra algorithm. The link-state database that the ABR maintains contains information about the network's topology and the state of its links, which is fundamental for OSPF's ability to perform efficient routing.

While other choices mention functions related to routing, they do not specifically capture the role of the ABR in OSPF. The ABR does not broadcast routing tables like distance vector protocols, it does not manage exterior gateway protocols, and it does not perform only distance vector routing—OSPF is a link-state protocol. Hence, maintaining a link-state database is the correct and pertinent function of an OSPF area border router.