R3303-HP HSR6800 Routers IP Multicast Configuration Guide

13
Configuring IGMP snooping
Overview
IGMP snooping is a multicast constraining mechanism that runs on Layer 2 devices to manage and
control multicast groups.
By analyzing received IGMP messages, an IGMP snooping-enabled Layer 2 device establishes
mappings between ports and multicast MAC addresses, and forwards multicast data based on these
mappings.
As shown in Figure 11, w
ithout IGMP snooping, a Layer 2 switch floods multicast packets out of all ports
but the incoming port. IGMP snooping enables a Layer 2 switch to forward multicast packets destined for
a known multicast group address out of only ports that have multicast receivers. This feature improves
bandwidth efficiency, enhances multicast security, and helps per-host accounting for multicast users.
IGMP snooping is supported only when the SAP module is operating in bridge mode.
Figure 11 Before and after IGMP snooping is enabled on the Layer 2 device
Basic concepts in IGMP snooping
This section lists the basic concepts in IGMP snooping.
IGMP snooping related ports
As shown in Figure 12, Router A connects to the multicast source, IGMP snooping runs on Router B and
Router C, and Host A and Host C are multicast receivers.