2.1 IGMP Snooping Overview
This section describes the functions and advantages of the IGMP snooping protocol.
Internet Group Management Protocol Snooping (IGMP snooping) is a Layer 2 multicast
protocol. The IGMP snooping protocol maintains information about the outgoing interfaces of
multicast packets by listening to multicast protocol packets exchanged between the router and
hosts. In this way, the IGMP snooping protocol manages and controls the forwarding of multicast
packets.
The IGMP snooping protocol forwards multicast information only to the specified receivers
through Layer 2 multicast. It has the following advantages:
l Reducing broadcast packets on Layer 2 networks, saving network bandwidth
l Enhancing the security of multicast information
l Performing accounting for each host independently
2.2 IGMP Snooping Supported by the S7700
This section describes IGMP snooping features supported by the S7700.
IGMP Snooping
The S7700 supports VLAN-based IGMP snooping.
IGMP snooping implements Layer 2 multicast and controls multicast data forwarding by
listening to multicast protocol packets sent between an upstream router and a downstream host
and maintaining downstream interface information.
You can configure user hosts to join a multicast group statically so that user hosts can steadily
receive multicast data packets.
You can also enable the S7700 to actively send IGMP Query messages so that the S7700 can
rapidly sense a Layer 2 network topology change and forward multicast data based on the new
topology, preventing multicast services from being interrupted.
Prompt Leave
When an interface of the S7700 receives an IGMP Leave message to leave a specified multicast
group, the S7700 deletes the interface from the downstream interface list of this multicast group
immediately. This is called prompt leave of a multicast group member. This feature is used in
the multicast IPTV scenario where one interface of the S7700 is commonly connected to only
one user host. Therefore, the prompt leave function shortens the speed at which the user switches
channels.
IGMP snooping prompt leave has the following advantages:
l Reducing response delay
l Saving the network bandwidth that is used by various types of messages
Quidway S7700 Smart Routing Switch
Configuration Guide - Multicast 2 IGMP Snooping Configuration
Issue 01 (2011-07-15) Huawei Proprietary and Confidential
Copyright © Huawei Technologies Co., Ltd.
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