3Com Switch 8800 Advanced Software V5 Configuration Guide

Introduction to OSPF 311
Figure 90 OSPF packet format
OSPF packet header
OSPF packets are classified into five types that have the same packet header, as
shown below.
Figure 91 OSPF packet header
■ Version: OSPF version number, which is 2 for OSPFv2.
■ Type: OSPF packet type from 1 to 5, corresponding with hello, DD, LSR, LSU
and LSAck respectively.
■ Packet length: Total length of the OSPF packet in bytes, including the header
■ Router ID: ID of the advertising router
■ Area ID: ID of the area where the advertising router resides
■ Checksum: Checksum of the message
■ Autype: Authentication type from 0 to 2, corresponding with
non-authentication, simple (plaintext) authentication and MD5 authentication
respectively.
■ Authentication: Information determined by authentication type, which is not
defined for authentication type 0, password information for authentication
type 1, information about Key ID, MD5 authentication data length and
sequence number for authentication type 2.
n
MD5 authentication data is added following an OSPF packet rather than
contained in the Authentication field.
Hello packet
A router sends hello packets periodically to neighbors to find and maintain
neighbor relationships and to elect DR/BDR, including information about values of
timers, DR, BDR and neighbors already known. The format is shown below:
IP header OSPF packet header Number of LSAs LSA header LSA Data
Version Type
Router ID
Area ID
Checksum AuType
Packet length
Authentication
Authentication
0715 31