Explains the IGMP snooping querier function in Cisco APIC for managing multicast traffic when PIM is not enabled on an interface.
An IGMP snooping querier function is a network mechanism that
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sends membership queries to trigger IGMP report messages from hosts wanting to receive IP multicast traffic
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establishes appropriate forwarding by listening to IGMP reports, and
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performs querier election as described in RFC 2236 when multiple queriers exist.
IGMP snooping querier configuration in APIC
When PIM is not enabled on an interface because the multicast traffic does not need to be routed, you must configure an IGMP snooping querier function to send membership queries. In APIC, within the IGMP Snoop policy, you define the querier in a bridge domain that contains multicast sources and receivers but no other active querier.
Cisco ACI has by default, IGMP snooping enabled. Additionally, if the Bridge Domain subnet control has "querier IP" selected, then the leaf switch behaves as a querier and starts sending query packets. Querier on the ACI leaf switch must be enabled when the segments do not have an explicit multicast router (PIM is not enabled). On the Bridge Domain where the querier is configured, the IP address used must be from the same subnet where the multicast hosts are configured.
The IP address for the querier should not be a broadcast IP address, multicast IP address, or 0 (0.0.0.0).
When an IGMP snooping querier is enabled, it sends out periodic IGMP queries that trigger IGMP report messages from hosts that want to receive IP multicast traffic. IGMP snooping listens to these IGMP reports to establish appropriate forwarding.
The IGMP snooping querier performs querier election as described in RFC 2236. Querier election occurs in these configurations:
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When there are multiple switch queriers configured with the same subnet on the same VLAN on different switches.
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When the configured switch querier is in the same subnet as with other Layer 3 SVI queriers.