In neighbor states Exchange or Loading, the Link state request list contains a list of those link state advertisements that need to be obtained from the neighbor. To request these advertisements, a router sends the neighbor the beginning of the Link state request list, packaged in a Link State Request packet.
When the neighbor responds to these requests with the proper Link State Update packet(s), the Link state request list is truncated and a new Link State Request packet is sent. This process continues until the Link state request list becomes empty. Unsatisfied Link State Request packets are retransmitted at intervals of RxmtInterval. There should be at most one Link State Request packet outstanding at any one time.
When the Link state request list becomes empty, and the neighbor state is Loading (i.e., a complete sequence of Database Description packets has been sent to and received from the neighbor), the Loading Done neighbor event is generated.