IGMP - Snooping Querier Election

An IGMP Snooping Querier is a network function involved in the management of multicast traffic when using IGMP in conjunction with IGMP snooping on a switch.

If there are multiple switches configured to function as a querier, a querier election takes place.

Query messages are used to elect the IGMP querier as follows:

1. At startup, IGMPv2 devices broadcast a general query message to the all-systems group address (224.0.0.1), using their interface address as the source IP address in the message.
2. Upon receiving a general query message, an IGMPv2 device compares the source IP address in the message to its own interface address. The device with the lowest IP address on the subnet is designated as the IGMP querier.
3. All other devices (except the elected querier) initiate their query timer, which is reset each time they receive a general query from the IGMP querier. If this timer expires, it suggests that the IGMP querier is no longer operational, prompting a new election to select a replacement. The standard setting for this timer is twice the length of the query interval.

Links:

https://forum.networklessons.com/t/igmp-snooping-without-router/1342/76?u=lagapidis

https://forum.networklessons.com/t/igmp-snooping-without-router/1342

https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst3850/software/release/37e/multicast/configuration_guide/b_mc_37e_3850_cg/b_mc_3e_3850_cg_chapter_0100.pdf