LevelOne GEL-2670, User Manual, Page: 151 / 320

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HAPTER
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| Configuring the Switch
IGMP Snooping
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IGMP S
NOOPING
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).
C
ONFIGURING
G
LOBAL
AND
P
ORT
-R
ELATED
S
ETTINGS FOR
IGMP
S
NOOPING
Use the IGMP Snooping Configuration page to configure global and port-
related settings which control the forwarding of multicast traffic. 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.
If multicast routing is not supported on other switches in your network, you
can use IGMP Snooping and IGMP Query to monitor IGMP service requests
passing between multicast clients and servers, and dynamically configure
the switch ports which need to forward multicast traffic.
Multicast routers use information from IGMP snooping and query reports,
along with a multicast routing protocol such as DVMRP or PIM, to support
IP multicasting across the Internet.
P
ATH
Advanced Configuration, IPMC, IGMP Snooping, Basic Configuration