In OSPF, the packet type used to request specific link-state advertisements from a neighbor is the Link State Request (LSR) packet. Therefore, option B is correct. During database synchronization, OSPF neighbors first discover each other with Hello packets, then exchange summaries of their databases using Database Description (DD) packets. If one router finds that it is missing certain LSAs or has older versions, it sends an LSR packet to request the needed LSAs from its neighbor.
The neighbor then responds with a Link State Update (LSU) packet containing the requested LSAs. Finally, the receiving router confirms proper receipt with a Link State Acknowledgment (LSAck) packet. HCIA-Datacom emphasizes understanding the roles of these five OSPF packet types because they are central to neighbor formation, adjacency establishment, and LSDB synchronization. This question specifically tests whether the learner can distinguish between the request packet (LSR) and the update packet (LSU). The router does not use a DD packet to request detailed LSA content; DD packets provide database summaries, while LSR packets explicitly request the LSAs that are needed.
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