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| Multicast Filtering
Layer 2 IGMP (Snooping and Query)
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CONFIGURING IGMP
SNOOPING AND QUERY
PARAMETERS
Use the Multicast > IGMP Snooping > General page to configure the switch
to forward multicast traffic. Based on the IGMP query and report
messages, the switch forwards multicast traffic only to the ports that
request it. This prevents the switch from broadcasting the traffic to all
ports and possibly disrupting network performance.
CLI REFERENCES
◆ "IGMP Snooping" on page 849
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 the multicast filters
accordingly.
N
OTE
:
If unknown multicast traffic enters a VLAN which has been
configured with a router port, the traffic is forwarded to that port. However,
if no router port exists on the VLAN, the traffic is dropped if unregistered-
flooding is disabled (default behavior), or flooded throughout the VLAN if
unregistered-flooding is enabled (see “Unregistered Data Flood” in the
Command Attributes section).
◆ IGMP Querier – 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 upstream multicast switch/router to ensure that it will continue to
receive the multicast service.
N
OTE
:
Multicast routers use this 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.
PARAMETERS
These parameters are displayed:
◆ IGMP Snooping Status – When enabled, the switch will monitor
network traffic to determine which hosts want to receive multicast
traffic. This is referred to as IGMP Snooping. (Default: Disabled)
When IGMP snooping is enabled globally, the per VLAN interface
settings for IGMP snooping take precedence (see "Setting IGMP
Snooping Status per Interface" on page 451).
When IGMP snooping is disabled globally, snooping can still be
configured per VLAN interface, but the interface settings will not take
effect until snooping is re-enabled globally.
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