LSR (Link State Request / Type3 OSPF Packets) is simply a request as obvious from its name. After DBD phase for first time, routers keep on sending LSR to keep the LSDB in sync.     Consider the simple below topology with two Routers: After the Hello & DBD, Requests are made from Routers to query the missing Database Parts. It is obvious from the below detail, spend some time with it to understand it fully:     Related