OSPF Packet Types

There are five types of OSPF packet types. The following figure describe the different types of OSPF

  1. Hello - Hello packets are used to establish and maintain adjacency with other OSPF routers. The hello protocol is discussed in detail in the next topic.

  2. DBD - The Database Description (DBD) packet contains an abbreviated list of the sending router's link-state database and is used by receiving routers to check against the local link-state database.

  3. LSR - Receiving routers can then request more information about any entry in the DBD by sending a Link-State Request (LSR).

  4. LSU - Link-State Update (LSU) packets are used to reply to LSRs as well as to announce new information. LSUs contain seven different types of Link-State Advertisements (LSAs).

  5. LSAck - When an LSU is received, the router sends a Link-State Acknowledgement (LSAck) to confirm receipt of the LSU.

OSPF packet Type 1 is the OSPF Hello packet. Hello packets are used to:

  • Discover OSPF neighbors and establish neighbor adjacencies.

  • Advertise parameters on which two routers must agree to become neighbors.

  • Elect the Designated Router (DR) and Backup Designated Router (BDR) on multiaccess networks like Ethernet and Frame Relay.