Multicast Filtering
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Instruction Manual - NXA-ENET8-POE+
Only IGMPv3 hosts can request service from a specific multicast source. When downstream hosts request service from a specific
source for a multicast service, these sources are all placed in the Include list, and traffic is forwarded to the hosts from each of
these sources. IGMPv3 hosts may also request that service be forwarded from any source except for those specified. In this case,
traffic is filtered from sources in the Exclude list, and forwarded from all other available sources.
NOTE:
When the switch is configured to use IGMPv3 snooping, the snooping version may be downgraded to version 2 or version 1,
depending on the version of the IGMP query packets detected on each VLAN.
NOTE:
IGMP snooping will not function unless a multicast router port is enabled on the switch. This can accomplished in one of two
ways. A static router port can be manually configured (see the Specifying Static Interfaces for a Multicast Router
.) Using this method, the router port is never timed out, and will continue to function until explicitly removed. The other
method relies on the switch to dynamically create multicast routing ports whenever multicast routing protocol packets or IGMP query
packets are detected on a port.
NOTE:
A maximum of up to 1023 multicast entries can be maintained for IGMP snooping. Once the table is full, no new entries are
learned. Any subsequent multicast traffic not found in the table is dropped if unregistered-flooding is disabled (default behavior) and
no router port is configured in the attached VLAN, or flooded throughout the VLAN if unregistered-flooding is enabled (see the
Configuring IGMP Snooping and Query Parameters
).
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 236). 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 238).
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.