Asante Technologies 40240/40480-10G Chapter 15: Multicast Filtering

This switch can use Internet Grou p Management
Protocol (IGMP) to filter multicast traffic. IGMP
Snooping can be used to passively mon itor or
“snoop” on exchanges between attached hosts
and an IGMP-enabled device, most commonly a
multicast router. In this way, the switc h can discover the ports that want to join a
multicast group, and set its filters ac cordingly.
If there is no multicast route r attached to the local subnet, multicast traffic and query
messages may not be received by the switch. In this case (Layer 2) IGMP Query
can be used to actively as k the attac hed hosts if they want to r eceive a specific
multicast service. IGMP Query thereby identifies the ports containing hosts
requesting to join the service and sends d ata out to those ports only. It then
propagates the service r equest up to any neighboring multicast switch/route r to
ensure that it will continue to receive the multicast service.
The purpose of IP multicast filtering is to optimize a switched network’s
performance, so multicast packets will only be forwarded to those ports containing
multicast group hosts or multicast routers/switche s, instead of flooding traffic to all
ports in the subnet (VLAN).
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Chapter 15: Multicast Filtering
Multicasting is used to support real-time
applications such as videoconferencing or
streaming audio. A multicast server does not have
to establish a separat e connection with each
client. It merely broadcasts its service to the
network, and any hosts that want to receive the
multicast register with their local multicast switch/
router. Although this approach reduces the
network overhead required by a multicast server,
the broadcast traffic must be carefully p runed at
every multicast switch/route r it passes through to
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Unicast
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Multicast
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