OSPF Packet Header

All OSPF packets have a common 24-byte header that contains all information necessary to determine whether OSPF should accept the packet. The header consists of the following fields:

• Version number—The current OSPF version number. This can be either 2 or 3.
• Type—Type of OSPF packet.
• Packet length—Length of the packet, in bytes, including the header.
• Router ID—IP address of the router from which the packet originated.
• Area ID—Identifier of the area in which the packet is traveling. Each OSPF packet is associated with a single area. Packets traveling over a virtual link are labeled with the backbone area ID, 0.0.0.0. You configure the area ID as described in Configuring the Backbone Area and Other Areas.
• Checksum—Fletcher checksum.
• Authentication—Authentication scheme and authentication information. You configure authentication as described in Configuring Authentication for OSPFv2.

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