Chapter 16
| Multicast Filtering
Layer 2 IGMP (Snooping and Query)
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If immediate leave is not used, a multicast router (or querier) will send a group-
specific query message when an IGMPv2 group leave message is received. The
router/querier stops forwarding traffic for that group only if no host replies to
the query within the specified time out period. Note that this time out is set to
Last Member Query Interval * Robustness Variable (fixed at 2) as defined in RFC
2236.
If immediate leave is enabled, the switch assumes that only one host is
connected to the interface. Therefore, immediate leave should only be enabled
on an interface if it is connected to only one IGMP-enabled device, either a
service host or a neighbor running IGMP snooping.
This attribute is only effective if IGMP snooping is enabled, and IGMPv2
snooping is used.
◆ Multicast Router Discovery – MRD is used to discover which interfaces are
attached to multicast routers. (Default: Disabled)
◆ General Query Suppression – Suppresses general queries except for ports
attached to downstream multicast hosts. (Default: Disabled)
By default, general query messages are flooded to all ports, except for the
multicast router through which they are received.
If general query suppression is enabled, then these messages are forwarded
only to downstream ports which have joined a multicast service.
◆ Proxy Reporting – Enables IGMP Snooping with Proxy Reporting. (Default:
Based on global setting)
When proxy reporting is enabled with this command, the switch performs
“IGMP Snooping with Proxy Reporting” (as defined in DSL Forum TR-101, April
2006), including last leave, and query suppression.
Last leave sends out a proxy query when the last member leaves a multicast
group, and query suppression means that specific queries are not forwarded
from an upstream multicast router to hosts downstream from this device.
Rules Used for Proxy Reporting
When IGMP Proxy Reporting is disabled, the switch will use a null IP address for
the source of IGMP query and report messages unless a proxy query address
has been set.
When IGMP Proxy Reporting is enabled, the source address is based on the
following criteria:
■
If a proxy query address is configured, the switch will use that address as
the source IP address in general and group-specific query messages sent to
downstream hosts, and in report and leave messages sent upstream from
the multicast router port.
■
If a proxy query address is not configured, the switch will use the VLAN’s IP
address as the IP source address in general and group-specific query
messages sent downstream, and use the source address of the last IGMP
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