System information

2-80
Configuring the Switch
2
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).
Layer 2 IGMP (Snooping and Query)
IGMP Snooping and Query – If multicast routing is not supported on other switches
in your network, you can use IGMP Snooping and IGMP Query (page 2-81) to
monitor IGMP service requests passing between multicast clients and servers, and
dynamically configure the switch ports which need to forward multicast traffic.
Static IGMP Router Interface – If IGMP snooping cannot locate the IGMP querier,
you can manually designate a known IGMP querier (i.e., a multicast router/switch)
connected over the network to an interface on your switch (page 2-83). This
interface will then join all the current multicast groups supported by the attached
router/switch to ensure that multicast traffic is passed to all appropriate interfaces
within the switch.
Unicast
Flow
Multicast
Flow