Protocol Overview; Dr Election; Simplified Hello Message Format - Alcatel OmniSwitch 6624 Troubleshooting Manual

Troubleshooting PIM-SM

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.
192.168.11.3/24
Hello pkt
Hello pkt
192.168.11.2/24

Simplified Hello Message Format

IP: ----- IP Header -----
IP: Protocol
IP: Source address
IP: Destination address = [224.0.0.13]
OmniSwitch Troubleshooting Guide
Ethernet
= 103 (PIM)
= [192.168.11.1]
September 2005
192.168.11.4/24
Hello pkt
192.168.11/24
192.168.11.1/24
Hello pkt
Protocol Overview
segment
page 16-3