What type of message is used to acknowledge receipt of LSAs in OSPF?

In OSPF (Open Shortest Path First), when a router receives a Link State Advertisement (LSA) from its neighbor, it sends an acknowledgment back to confirm that it has received the LSA. This acknowledgment message is known as the LSAck (Link State Acknowledgment). The use of LSAck messages is a critical aspect of OSPF's reliability, ensuring that routers can correctly track the LSAs they have received and recognize any that may need to be retransmitted.

LSAs themselves are the actual data structure used to convey the topology and routing information, while DBD (Database Description) messages are used during the initial discovery process of OSPF to share summaries of the LSAs. LSU (Link State Update) messages are the actual transport vehicle for LSAs between routers, but they do not serve the purpose of acknowledging receipt. Thus, the LSAck message is essential for maintaining the accurate synchronization of the link-state database among OSPF routers.