said by cramer:It's a bug. It simply doesn't handle multicast correctly. (common failing of wireless gear.)
IGMP snooping allows the device doing the snooping to filter multicast to what's actually needed on a link. Without this "hack", all multicast traffic is flooded as broadcast traffic.
My understanding is IGMP snooping trades CPU for bandwidth.
It builds a table of what is listening for multicast and then if something sends a multicast it only sends it to those listening, thus saving bandwidth on the non-listening ports. (kind of like a switch to a hub)
but on the AP1242AG (possibly other models too, and possibly fixed in a newer IOS) it just dead ends multicast at the radio, so even another wifi device won't hear the multicast.
By turning snooping off (the default is on, thus why the command didn't show up in the running config, but the no form does show up in the running config)
Its just a matter of a bug that IGMP snooping doesn't work on the AP.