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 IP Multicast Group page.
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.
The IGMP/MLD Snooping querier resumes sending general query messages if it does hear another querier for the following interval:
Query passive interval = Robustness * Query Interval + 0.5*Query Response Interval.
NOTE It is recommended to disable IGMP/MLD Querier election mechanism if there is an IPM Multicast router on the VLAN.