What does a Database Description (DBD) message contain?

A Database Description (DBD) message is a component of the Open Shortest Path First (OSPF) protocol, which is used to summarize the information contained in a router's link-state database. The primary purpose of a DBD message is to briefly list the link-state advertisements (LSAs) that a router has in its database, providing other routers with an overview of the network topology without needing to include all the specific details of those LSAs at that moment. This allows for efficient synchronization between OSPF routers by minimizing the amount of data that needs to be exchanged initially.

When routers start communicating in OSPF, they use DBD messages to determine which LSAs they already have and which ones they might be missing. This process helps optimize the OSPF operation and ensures that each router has a consistent view of the network's topology.

The other choices, while related to link-state routing processes, do not accurately describe the content of a DBD message. For example, a request for link-state information would typically be communicated by a different type of message, and link-state advertisements are specific updates or notifications that do not summarize the entire database. Therefore, the correct answer is the summary of the entire link-state database, as this reflects