During which process does a router compare its topology with that of another router?

The correct answer is the database description process. During this phase, routers build and maintain a synchronized link-state database (LSDB) by exchanging summaries of their link-state information. When a router sends a database description packet, it includes information about the types of link-state advertisements (LSAs) it holds, allowing the receiving router to determine whether it has the most up-to-date information.

This comparison is crucial as it helps routers identify which LSAs they need to request from each other, leading to the overall updating of the link-state database. The database description packets ensure that both routers have a consistent view of the network topology, which is vital for accurate and efficient routing.

In contrast, the other processes listed have different purposes: link-state updates are concerned with sending the actual LSAs after the initial comparison, hello packet exchanges are used primarily to establish and maintain OSPF neighbor relationships, and best path selection occurs after the LSDB is synchronized and involves determining the optimal route to each destination based on various metrics.