Ospf Packet Formats - D-Link DES-3350SR User Manual

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
•
Link-State Update packet
•
Link-State Acknowledgment packet
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:
Field
Version No.
Type
Packet Length
Router ID
Area ID
Checksum
Authentication Type
Authentication
Hello Packet
Hello packets are OSPF packet type 1. They are sent periodically on all interfaces, including virtual links, in order to establish and
maintain neighbor relationships. In addition, Hello Packets are multicast on those physical networks having a multicast or
broadcast capability, enabling dynamic discovery of neighboring routers.
D-Link DES-3350SR Standalone Layer 3 Switch
OSPF Packet Header
Type
Version No.
Checksum
Figure 9 - 16. OSPF Packet Header Format
Description
The OSPF version number
The OSPF packet type. The OSPF packet types are as follows: Type
Description Hello Database Description Link-State Request Link-State
Update Link-State Acknowledgment
The length of the packet in bytes. This length includes the 24-byte
header.
The Router ID of the packet's source.
A 32-bit number identifying the area that this packet belongs to. All
OSPF packets are associated with a single area. Packets traversing a
virtual link are assigned the backbone Area ID of 0.0.0.0
A standard IP checksum that includes all of the packet's contents
except for the 64-bit authentication field.
The type of authentication to be used for the packet.
A 64-bit field used by the authentication scheme.
Packet Length
Router ID
Area ID
Authentication Type
Authentication
Authentication
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