Installation manual

3-243
SIGNAMAX LLC • www.signamax.eu
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.
This 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 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 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 only. It then propagates the service request up to any
neighboring multicast switch/router 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/switches, instead of flooding traffic to all ports in the subnet (VLAN).
You can also configure a single network-wide multicast VLAN shared by hosts residing in
other standard or private VLAN groups, preserving security and data isolation “Multicast
VLAN Registration” on page 3-257.
Unicast
Flow
Multicast
Flow