90
•
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. 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
As shown in Figure 27, a router sends hello packets periodically to neighbors to find and
maintain neighbor relationships, and to elect the DR or BDR, including information about values
of timers, DR, BDR, and neighbors already known.
Figure 27
Hello packet format
...
Network mask
HelloInterval
Options
Rtr Pri
RouterDeadInterval
Designated router
Backup designated router
Neighbor
Version
1
Router ID
Area ID
Checksum
AuType
Packet length
Authentication
Authentication
0
7
15
31
Neighbor
