OSPF has five different types of messages it uses to exchange link state information between other neighbors in the network. Link State Advertisements are the messages used to communicate these databases between neighbors.
Hello Messages – this message is used to discover neighbors and brings the neighborship to a 2 way state, also monitors the neighbors continuous livlieness.
Database Description (DD or DBD) – this message is used to exchange LSA headers during topology exchange so a router would know the list of that neighbors LSAs and their versions.
Link State Request (LSR) – this is a message that identifies one or more LSAs to a neighbor to supply the details about that specific LSA.
Link State Update (LSU) – This message contains all the details for a specific LSA in response to the LSR request.
Link State Acknowledgement (LSAck) – this message is sent to confirm receipt of an LSU message.