3Com Switch 4800G 24-Port - Page 284

284 CHAPTER 28: OSPF CONFIGURATION
Figure 82 Hello packet format
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.
■ Rtr Pri: Router priority. A value of 0 means the router cannot become the
DR/BDR.
■ RouterDeadInterval: Time before declaring a silent router down. If two routers
have different time values, they cannot become neighbors.
■ Designated Router: IP address of the DR interface.
■ Backup Designated Router: IP address of the BDR interface
■ 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 LSA). The LSA header occupies small part of an LSA
to reduce traffic between routers. The recipient checks whether the LSA is
available using the LSA header.
The DD 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