3Com S7906E Configuration Manual page 644

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. It is not defined for authentication
type 0. It is defined as password information for authentication type 1, and defined as Key ID, MD5
authentication data length and sequence number for authentication type 2.
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 the DR/BDR, including information about values of timers, DR, BDR and neighbors already known.
The format is shown below:
Figure 1-10 Hello packet format
0 7
Version
Checksum
HelloInterval
Major fields:
Network mask: Network mask associated with the router's sending interface. If two routers have
different network masks, they cannot become neighbors.
HelloInterval: Interval for sending hello packets. If two routers have different intervals, they cannot
become neighbors.
15
1
Router ID
Area ID
Authentication
Authentication
Network mask
Options
RouterDeadInterval
Designated router
Backup designated router
Neighbor
Neighbor
1-11
Packet length
AuType
Rtr Pri
31