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When IGMP/MLD Snooping is enabled globally or on a VLAN, all IGMP/MLD packets are
forwarded to the CPU. The CPU analyzes the incoming packets, and determines the following:
•
Which ports are asking to join which Multicast groups on what VLAN.
•
Which ports are connected to Multicast routers (Mrouters) that are generating IGMP/
MLD queries.
•
Which ports are receiving PIM, DVMRP, or IGMP/MLD query protocols.
These VLANs are displayed on the
Ports, asking to join a specific Multicast group, issue an IGMP/MLD report that specifies
which group(s) the host wants to join. This results in the creation of a forwarding entry in the
Multicast Forwarding Data Base.
IGMP Snooping Querier
The IGMP/MLD Snooping Querier is used to support a Layer 2 Multicast domain of snooping
switches in the absence of a Multicast router. For example, where Multicast content is
provided by a local server, but the router (if one exists) on that network does not support
Multicast.
The device can be configured to be an IGMP Querier as a backup querier, or in situation where
a regular IGMP Querier does not exist. The device is not a full capability IGMP Querier.
If the device is enabled as an IGMP Querier, it starts after 60 seconds have passed with no
IGMP traffic (queries) detected from a Multicast router. In the presence of other IGMP
Queriers, the device might (or might not) stop sending queries, based on the results of the
standard querier selection process.
The speed of IGMP/MLD querier activity must be aligned with the IGMP/MLD-snooping-
enabled switches. Queries must be sent at a rate that is aligned to the snooping table aging
time. If queries are sent at a rate lower than the aging time, the subscriber cannot receive the
Multicast packets. This is performed in the
If the IGMP/MLD querier election mechanism is disabled, then the IGMP/MLD Snooping
Querier delays sending general query messages after its enabling for 60 seconds. If there is no
other querier, it starts to send general query messages. It stops sending general query messages
if it detects another querier.
Cisco Sx350, SG350X, SG350XG, Sx550X & SG550XG Series Managed Switches, Firmware Release 2.2.5.x
IGMP/MLD Snooping IP Multicast Group
IGMP/MLD Snooping IP Multicast Group
Multicast
Multicast Forwarding Overview
page.
page.
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