Igmp Snooping - EnGenius EWS Series User Manual

IGMP Snooping

Internet Group Management Protocol (IGMP) Snooping allows a Switch to forward multicast traffic
intelligently. Multicasting is used to support real-time applications such as video conferencing or
streaming audio. A multicast server does not have to establish a separate connection with each client. It
merely broadcasts its service to the network, and any host that wishes to receive the multicast register
with their local multicast Switch.
A multicast group is a group of end nodes that want to receive multicast packets from a multicast
application. After joining a multicast group, a host node must continue to periodically issue reports to
remain a member. Any multicast packets belonging to that multicast group are then forwarded by the
Switch from the port.
A Switch supporting IGMP Snooping can passively snoop on IGMP Query, Report, and Leave packets
transferred between IP Multicast switches and IP Multicast hosts to determine the IP Multicast group
membership. IGMP Snooping checks IGMP packets passing through the network and configures
multicasting accordingly. Based on the IGMP query and report messages, the Switch forwards traffic only
to the ports that request the multicast traffic. It enables the Switch to forward packets of multicast
groups to those ports that have validated host nodes. The Switch can also limit flooding of traffic to
IGMP designated ports. This improves network performance by restricting the multicast packets only to
switch ports where host nodes are located. IGMP Snooping significantly reduces overall Multicast traffic
passing through your Switch. Without IGMP Snooping, Multicast traffic is treated in the same manner as
a broadcast transmission, which forwards packets to all ports on the network.
IGMPv1 Defined in RFC 1112. An explicit join message is sent to the Switch, but a timeout is
used to determine when hosts leave a group.
IGMPv2 Defined in RFC 2236. Adds an explicit leave message to the join message so that
Switch can more easily determine when a group has no interested listeners on a LAN.
IGMPv3 Defined in RFC 3376. Support for a single source of content for a multicast group.
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