You only need one of them configured on the switch were your core AV device is that discovers all the A/V devices on the network(and put the querier on the correct vlan). You also only need the IGMP querier if they are on separate switches. We had a Shure vendor tech support try and tell us that the Mics didn't support vlans but that was just them trying to blame our network for audio streams making it to the core device but getting silently ignored(when they had been working for years before without issue). ... View more