H3C Technologies H3C S7500E Series Switches - Manual (Page 80)

4-11
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 4-10 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
Major fields:
z Network mask: Network mask associated with the router’s sending interface. If two routers have
different network masks, they cannot become neighbors.
z HelloInterval: Interval for sending hello packets. If two routers have different intervals, they cannot
become neighbors.
z Rtr Pri: Router priority. A value of 0 means the router cannot become the DR/BDR.
z RouterDeadInterval: Time before declaring a silent router down. If two routers have different time
values, they cannot become neighbors.
z Designated router: IP address of the DR interface.
z Backup designated router: IP address of the BDR interface
z Neighbor: Router ID of the neighbor router.
DD packet
Two routers exchange database description (DD) packets describing their LSDBs for database
synchronization, contents in DD packets including the header of each LSA (uniquely representing a