Configuring the ECN330-switch
352 1553-KDU 137 365 Uen D 2006-06-16
6.16 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 separate
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 pruned at every
multicast switch/router it passes through to ensure that traffic is only passed on
to the hosts which subscribed to this service.
Figure 144 Multicast Filtering Concept
The ECN330-switch can use Internet Group Management Protocol (IGMP) to
filter multicast traffic. IGMP Snooping can be used to passively monitor or
"snoop" on exchanges between attached hosts and an IGMP-enabled device,
most commonly a multicast router. In this way, the ECN330-switch can discover
the ports that want to join a multicast group, and set its filters accordingly.
If there is no multicast router attached to the local subnet, multicast traffic and
query messages may not be received by the ECN330-switch. In this case (Layer
2) IGMP Query can be used to actively ask the attached hosts if they want to
receive a specific multicast service. IGMP Query thereby identifies the ports
containing hosts requesting to join the service and sends data out to those ports
Unicast
Flow
Multicast
Flow
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