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Routing & Switching · Intermediate

OSPF Packet Types

The five OSPF packet types: Hello, Database Description (DBD), Link-State Request (LSR), Link-State Update (LSU) and Link-State Acknowledgment.

Definition

OSPFv2 and OSPFv3 use five packet types, all carried directly over IP protocol 89 (OSPFv2) or IPv6 next header 89. Type 1 Hello discovers and maintains neighbors; Type 2 DBD summarizes LSDB contents during ExStart/Exchange; Type 3 LSR asks for specific LSAs; Type 4 LSU carries LSAs; Type 5 LSAck acknowledges LSUs for reliable flooding.

Example

debug ip ospf adj shows DBD exchange during adjacency formation.

Exam tip

LSAs are carried inside LSU packets; an LSA is not a packet type itself.

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