H3C Technologies H3C S3100 Series Switches - Manual (Page 238)

Operation Manual – Multicast
H3C S3100-52P Ethernet Switch Chapter 2 IGMP Snooping Configuration
2-1
Chapter 2 IGMP Snooping Configuration
2.1 Overview
2.1.1 IGMP Snooping Fundamentals
Internet group management protocol snooping (IGMP Snooping) is a multicast control
mechanism running on Layer 2 switches. It is used to manage and control multicast
groups.
When the IGMP messages transferred from the hosts to the router pass through the
Layer 2 switch, the switch uses IGMP Snooping to analyze and process the IGMP
messages, as shown in Table 2-1.
Table 2-1
IGMP message processing on the switch
Received
message type
Sender Receiver Switch processing
IGMP host report
message
Host Switch
Add the host to the
corresponding multicast group.
IGMP leave
message
Host Switch
Remove the host from the
multicast group.
By listening to IGMP messages, the switch establishes and maintains MAC multicast
address tables at data link layer, and uses the tables to forward the multicast packets
delivered from the router.
As shown in Figure 2-1, multicast packets are broadcast at Layer 2 when IGMP
Snooping is disabled and multicast (not broadcast) at Layer 2 when IGMP Snooping is
enabled.