Chapter 16
| Multicast Filtering
Layer 2 IGMP (Snooping and Query)
– 469 –
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 “Specifying Static Interfaces for a Multicast Router” on
page 473). 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 255 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
“Configuring IGMP Snooping and Query Parameters” on page 470).
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 473). 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 476).
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.
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