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BLADEOS 6.5.2 Application Guide
250 Chapter 18: Internet Group Management Protocol BMD00220, October 2010
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 IPv4 Multicast router. After the pathway is
established, the switch blocks the IPv4 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 IPv4 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 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.
The G8124 supports the following:
IGMP version 1, 2, and 3
128 Mrouters
Note – Unknown multicast traffic is sent to all ports if the flood option is enabled and no
Membership Report was learned for that specific IGMP group. To enable or disable IGMP flood,
use the following command:
RS G8124(config)# [no] ip igmp snoop flood