Igmp Snooping Introduction; Overview; Fastleave - HP GbE2c - Blc Layer 2/3 Fiber SFP Option Application Manual

IGMP Snooping
Introduction
IGMP Snooping allows the switch to forward multicast traffic only to those ports that request it. IGMP Snooping
prevents multicast traffic from being flooded to all data ports. The switch learns which server hosts are interested in
receiving multicast traffic, and forwards it only to ports connected to those servers.
The following topics are discussed in this chapter:

Overview

FastLeave

IGMP Filtering
Static Multicast Router
IGMP Snooping Configuration example
Overview
Internet Group Management Protocol (IGMP) is used by IP Multicast routers to learn about the existence of host group
members on their directly attached subnet (see RFC 2236). The IP Multicast routers get this information by
broadcasting IGMP Query Reports and listening for IP hosts reporting their host group memberships. This process is
used to set up a client/server relationship between an IP Multicast source that provides the data streams and the
clients that want to receive the data.
IGMP Snooping conserves bandwidth. With IGMP Snooping, the switch learns which ports are interested in receiving
multicast data, and forwards multicast data only to those ports. In this way, other ports are not burdened with
unwanted multicast traffic.
The switch currently supports snooping for IGMP version 1 and version 2.
The switch can sense IGMP Membership Reports from attached host servers and act as a proxy to set up a dedicated
path between the requesting host and a local IP Multicast router. After the pathway is established, the switch blocks
the IP Multicast stream from flowing through any port that does not connect to a host member, thus conserving
bandwidth.
The client-server path is set up as follows:
An IP Multicast Router (Mrouter) sends Membership Queries to the switch, which forwards them to all ports in a
given VLAN.
Hosts that want to receive the multicast data stream send Membership Reports to the switch, which sends a
proxy Membership Report to the Mrouter.
The switch sets up a path between the Mrouter and the host, and blocks all other ports from receiving the
multicast.
Periodically, the Mrouter sends Membership Queries to ensure that the host wants to continue receiving the
multicast. If the host fails to respond with a Membership Report, the Mrouter stops sending the multicast to that
path.
The host can send a Leave report to the switch, which sends a proxy Leave report to the Mrouter. The multicast
path is terminated immediately.
FastLeave
When the switch with IGMP Snooping enabled receives an IGMPv2 leave message, it sends a Group-Specific Query
to determine if any other devices in the same group (and on the same port) are still interested in the specified
multicast group traffic. The switch removes the affiliated port from that particular group, if the following conditions
apply:
If the switch does not receive an IGMP Membership Report message within the query-response-interval
If no multicast routers have been learned on that port.
With FastLeave enabled on the VLAN, a port can be removed immediately from the port list of the group entry when
the IGMP Leave message is received, unless a multicast router was learned on the port.
Enable FastLeave only on VLANs that have only one host connected to each physical port.
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