FL SWITCH LM ...
5-2
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IGMP snooping A switch, which connects a multicast receiver with a router, can read and evaluate IGMP
information using the IGMP snooping method. IGMP snooping translates IP multicast group
addresses into multicast MAC addresses, so that the IGMP function can also be detected
by Layer 2 switches. The switch enters the MAC addresses of the multicast receivers, which
were obtained from the IP addresses by IGMP snooping, in its own multicast filter table.
Thus the switch filters multicast packets of known multicast groups and only forwards
packets to those ports to which corresponding multicast receivers are connected.
IGMP snooping can only be used on Layer 2 if all termination devices send IGMP
messages. The IP stack of multicast-compatible termination devices with applications
linked to a multicast address automatically sends the relevant membership reports.
IGMP snooping operates independently of the Internet Group Management Protocol
(IGMP).
5.2.1.1 Extended multicast filtering
When IGMP snooping is enabled, the switch automatically creates the corresponding
groups for unknown multicast data for which it has received no IGMP reports and for which
no multicast groups have been created. This multicast data is then forwarded to the querier,
e.g., if the querier port is automatically added to the group. If the switch is in fact the active
querier, this multicast is blocked at all ports. All subsequent IGMP reports for this group are
handled normally, i.e., this port is part of the multicast group.
5.2.1.2 "General Multicast Configuration" web page
This web page provides global settings for multicast support. Here, IGMP snooping can be
activated and an aging time can be specified for IGMP snooping information.
Figure 5-1 "General Multicast Configuration" web page
Please note that the switch supports 50 multicast groups at any given time.
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