Web Management Guide-R04

Table Of Contents
Chapter 14
| Multicast Filtering
Layer 2 IGMP (Snooping and Query for IPv4)
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the switch (page 584).
IGMP Snooping with Proxy Reporting – The switch supports last leave, and query
suppression (as defined in DSL Forum TR-101, April 2006):
When proxy reporting is disabled, all IGMP reports received by the switch are
forwarded natively to the upstream multicast routers.
Last Leave: Intercepts, absorbs and summarizes IGMP leaves coming from IGMP
hosts. IGMP leaves are relayed upstream only when necessary, that is, when the
last user leaves a multicast group.
Query Suppression: Intercepts and processes IGMP queries in such a way that
IGMP specific queries are never sent to client ports.
The only deviation from TR-101 is that the marking of IGMP traffic initiated by the
switch with priority bits as defined in R-250 is not supported.
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.