SMC Networks SMC7816M, SMC7816VSW F, 16-4, Configuring IGMP Snooping and Query Parameters

M ULTICAST F ILTERING
16-4
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 multicastin g, 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, along with a multicast
routing protocol such as DVMRP or PIM, to support IP
multicasting across the Internet.