Configuring the Switch

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Configuring IGMP Snooping and Query 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 the multicast filters accordingly.
Note: Unknown multicast traffic is flooded to all ports in the VLAN for several seconds
when first received. If a multicast router port exists on the VLAN, the traffic will
be filtered by subjecting it to IGMP snooping. If no router port exists on the
VLAN or the multicast filtering table is already full, the switch will continue
flooding the traffic into the VLAN.
•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.
•IGMP Leave Proxy – This function is only effective if IGMP snooping is enabled.
IGMP leave proxy suppresses all unnecessary IGMP leave messages so that the
non-querier switch forwards an IGMP leave packet only when the last dynamic
member port leaves a multicast group.
The leave-proxy feature does not function when a switch is set as the querier.
When the switch a non-querier, the receiving port is not the last dynamic member
port in the group, the receiving port is not a router port, and no IGMPv1 member
port exists in the group, the switch will generate and send a GS-query to the
member port which received the leave message, and then start the last member
query timer for that port.
When the conditions in the preceding item all apply, except that the receiving port
is a router port, then the switch will not send a GS-query, but will immediately start
the last member query timer for that port.
Command Attributes
•IGMP Status — When enabled, the switch will monitor network traffic to determine
which hosts want to receive multicast traffic. This is also referred to as IGMP
Snooping. (Default: Enabled)