OSPFv2 Packet Types

OSPFv2 uses five different types of packets when communicating with neighboring routers and requesting and sending Link-State Advertisements (LSAs). These packets are (briefly) described below and also shown in a packet capture from a lab environment (lab topology is shown in the bottom of the post). This is to explain the function of each packet and to show the packet format (in this case from a Wireshark capture of packets from two routers running IOS 15.4).

Hello (type code 1)

Used to discover neighbors, bring neighbors to a 2-Way state and functions as a keepalive between neighbors.

OSPFv2 Hello Packet

Database Description (type code 2)

Used to exchange LSA headers when initially exchanging the topology, so that neighbors have a list of the routers LSAs. Also known as a DD or DBD packet.

OSPFv2 DBD Packet

Link-State Request (type code 3)

Identifies at least one LSA that the sending router would like full details about. Also known as an LSR packet.

OSPFv2 LSR Packet

Link-State Update (type code 4)

Contains a fully detailed LSA. These are sent either in response to an LSR or in the event of a topology change (like a link failure, for example). Also known as an LSU packet.

OSPFv2 LSU Packet

Link-State Acknowledgment (type code 5)

Sent in acknowledgement of each received LSA. This makes the OSPF communication reliable between neighbors.

OSPFv2 LSAck Packet

The packets were captured on router R1 in the topology shown below. To capture all five different packet types the capture was done at the initial forming of the neighbor adjacency between R1 and R2.

OSPFv2 Topology