Layer 2 Igmp (Snooping And Query); Configuring Igmp Snooping And Query Parameters - SMC Networks 8124PL2 - annexe 1 Management Manual

Configuring the Switch
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 adjacent multicast switch/router to ensure that it will continue to
receive the multicast service.
Based on the group membership information learned from IGMP, a router/switch can
determine which (if any) multicast traffic needs to be forwarded to each of its ports.
At Layer 3, multicast routers use this information, along with a multicast routing
protocol such as DVMRP or PIM, to support IP multicasting across the Internet.
Note that IGMP neither alters nor routes IP multicast packets. A multicast routing
protocol must be used to deliver IP multicast packets across different subnetworks.
Therefore, when DVMRP or PIM routing is enabled for a subnet on this switch, you
also need to enable IGMP.

Layer 2 IGMP (Snooping and Query)

IGMP Snooping and Query — If multicast routing is not supported on other
switches in your network, you can use IGMP Snooping and IGMP Query
(page 3-162) to monitor IGMP service requests passing between multicast clients
and servers, and dynamically configure the switch ports which need to forward
multicast traffic.
Static IGMP Router Interface — If IGMP snooping cannot locate the IGMP querier,
you can manually designate a known IGMP querier (i.e., a multicast router/switch)
connected over the network to an interface on your switch (page 3-165). This
interface will then join all the current multicast groups supported by the attached
router/switch to ensure that multicast traffic is passed to all appropriate interfaces
within the switch.
Static IGMP Host Interface — For multicast applications that you need to control
more carefully, you can manually assign a multicast service to specific interfaces on
the switch (page 3-167).
IGMP Query (Layer 2 or 3) – IGMP Query can only be enabled globally at Layer 2,
but can be enabled for individual VLAN interfaces at Layer 3 (page 3-99). However,
note that Layer 2 query is disabled if Layer 3 query is enabled.

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
3-162