Protocol overview, Dr election, Simplified hello message format – Alcatel Carrier Internetworking Solutions 6648 User Manual
Page 265: Protocol overview -3, Dr election -3, Simplified hello message format -3
Troubleshooting PIM-SM
Protocol Overview
OmniSwitch Troubleshooting Guide
September 2005
page 16-3
Protocol Overview
DR Election
Hello messages are sent periodically between PIM neighbors. This informs routers which interface has
PIM neighbors. Hello messages are multicast packets using address 224.0.0.13, which corresponds to
ALL-PIM-ROUTERS group.
When a router receives a Hello message, it stores the IP address for that neighbor and determines the
Designated Router (DR) for that specific interface. The highest IP address system is elected DR. DR infor-
mation is refreshed on each Hello messages received. Holdtime parameter is the amount of time a receiver
must keep the neighbor reachable, in seconds.
Simplified Hello Message Format
IP: ----- IP Header -----
IP: Protocol = 103 (PIM)
IP: Source address = [192.168.11.1]
IP: Destination address = [224.0.0.13]
Ethernet
192.168.11/24
segment
192.168.11.1/24
192.168.11.2/24
192.168.11.3/24
192.168.11.4/24
Hello pkt
Hello pkt
Hello pkt
Hello pkt