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Alteon OS Application Guide
162
Chapter 10: IGMP 42C4911, January 2007
IGMP Snooping
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 ports. The switch learns
which server hosts are interested in receiving multicast traffic, and forwards it only to ports
connected to those servers.
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 can sense IGMP Membership Reports from attached clients 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 for-
wards 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 con-
tinue receiving the multicast. If a 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.