Specifications

Configuring the Switch
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Multicast Filtering
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
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 the hosts
which subscribed to this service.
This switch uses IGMP (Internet Group Management Protocol) to query for any
attached hosts that want to receive a specific multicast service. It 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. This
procedure is called multicast filtering.
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).
Configuring IGMP Snooping Parameters
You can configure the switch to forward multicast traffic intelligently. Based on the
IGMP query and report messages, the switch forwards traffic only to the ports that
request multicast traffic. This prevents the switch from broadcasting the traffic to all
ports and possibly disrupting network performance.
Command Usage
• IGMP Snooping – This switch can passively snoop on IGMP Query and Report
packets transferred between IP multicast routers/switches and IP multicast host
groups to identify the IP multicast group members. It simply monitors the IGMP
packets passing through it, picks out the group registration information, and
configures multicast filters accordingly.
• IGMP Query – A router, or multicast-enabled switch, can periodically ask their
hosts if they want to receive multicast traffic. If there is more than one router/switch
on the LAN performing IP multicasting, one of these devices is elected “querier”
and assumes the role of querying the LAN for group members. It then propagates
the service requests on to any adjacent multicast switch/router to ensure that it will
continue to receive the multicast service.
Note: Multicast routers use this information, along with a multicast routing protocol such
as DVMRP or PIM, to support IP multicasting across the Internet.