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DES-3326 Layer 3 Fast Ethernet Switch User’s Guide
Adjacencies on Point-to-Point Interfaces
OSPF Routers that are linked using point-to-point interfaces (such as serial links) will always form
adjacencies. The concepts of DR and BDR are unnecessary.
OSPF Packet Formats
All OSPF packet types begin with a standard 24-byte header and there are five packet types. The
header is described first, and each packet type is described in a subsequent section.
All OSPF packets (except for Hello packets) forward link-state advertisements. Link-State Update
packets, for example, flood advertisements throughout the OSPF routing domain.
• OSPF packet header
• Hello packet
• Database Description packet
• Link-State Request packet
• The Link-State Update packet
• Link-State Acknowledgment packet
The OSPF Packet Header
Every OSPF packet is preceded by a common 24-byte header. This header contains the information
necessary for a receiving router to determine if the packet should be accepted for further processing.
The format of the OSPP packet header is shown below:
OSPF Packet Header
Type
Packet Length
Router ID
Area ID
Checksum
Authentication Type
Authentication
Authentication
Version No.
Figure 5-25. OSPF Packet Header
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