packet format

• Version number - Identifies the OSPF version used
• Type - Identifies the OSPF packet type as one of the following:
  • Hello : established and maintains neighbor relationships
  • Database description : Describes the contents of the topological database. These messages are exchanged when an adjacency is initialized.
  • Link-state request : Request pieces of the topological database from neighbor routers. These messages are exchanged after a router discovers (by examining database-description packets) that parts of its topological database are outdated.
  • Link-state update : Responds to a link-state request packet. These messages also are used for the regular dispersal of LSAs. Several LSAs can be included within a single link-state update packet.
  • Link-state acknowledgment : Acknowledges link-state update packets.
• Packet length - Specifies the packet length, including the OSPF header, in bytes.
• Router ID - Identifies the source of the packet.
• Area ID - Identifies the area to which the packet belongs. All OSPF packets are associated with a single area.
• Checksum - Checks the entire packet contents for any damage suffered in transit.
• Authentication type - Contains the authentication type. All OSPF protocol exchanges are authenticated. The authentication type is configurable on per-area basis.
• Authentication - Contains authentication information.
• Data - Contains encapsulated upper-layer information.

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