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Chapter 16
| Multicast Filtering
Layer 2 IGMP (Snooping and Query)
Configuring IGMP
Snooping and Query
Parameters
Use the Multicast > IGMP Snooping > General page to configure the switch to
forward multicast traffic intelligently. 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.
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.
Note:
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 data flooding is disabled (default
behavior), or flooded throughout the VLAN if unregistered data flooding is enabled
(see "Unregistered Data Flooding" 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.
Note:
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
Interface" on page
540).
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.
◆
Proxy Reporting Status – Enables IGMP Snooping with Proxy Reporting.
(Default: Disabled)
"Setting IGMP Snooping Status per
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