Cisco 500 Series Administration Manual page 319

17
NOTE
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The following versions are supported:
• IGMP v1/v2/ v3
• MLD v1/v2
The device supports IGMP/MLD Snooping only on static VLANs. It does not
support IGMP/MLD Snooping on dynamic VLANs.
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 IGMP/MLD Snooping page.
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
IGMP/MLD Snooping Edit page.
Cisco 500 Series Managed Switch Administration Guide
Multicast
Multicast Forwarding