3Com Switch 8800 Advanced Software V5 Configuration Guide

312 CHAPTER 30: OSPF CONFIGURATION
Figure 92 Hello packet format
Major fields:
■ Network Mask: The network mask associated with the router’s sending
interface. If two routers have different network masks, they cannot become
neighbors.
■ HelloInterval: The interval between the router’s 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: The time value before declaring a silent router down. If
two routers have different time values of this kind, 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,
so reducing 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