What OSPF packet type does Router A send to Router B when it receives an LSA header not in its database?

When Router A receives an LSA (Link-State Advertisement) header that is not present in its database, it will respond with a Type 3 OSPF packet, which is known as the Link-State Request (LSR). This packet type is specifically used to request more information about the LSAs that the router needs in order to update its routing database.

In OSPF, when a router encounters an LSA it doesn’t recognize, it typically means that the LSA may contain information about new routes or changes in the topology that could affect the routing decisions. To maintain accurate and synchronized routing information within the OSPF area, the router issues a Link-State Request to solicit the specific LSAs it requires to fully understand the network topology and other routers' states.

By sending a Type 3 packet, Router A indicates that it requires further details about the specific LSA header it encountered, allowing it to become up-to-date with the latest network information. This action is crucial for effective OSPF operation, as maintaining an accurate and consistent view of the network among all routers is essential for optimal routing.