igmp snooping enable, but without groups

[jacnetoanbima]

How do switches, with igmp snooping enable, knows exactly which interfaces forward multicast traffic without a router in the environment end without enable "igmp snooping querier"? Note: when I run "sh ip igmp snooping groups" there aren't informations about multicast groups end with wireshark I don't receive broadcast with multicast address, but multicast applications are working. 

[Jon Marshall · Accepted solution]

The switch will not change the multicast mac address to a broadcast mac address but it will simply flood the multicast to all ports in the vlan (other than the one it was received on).

One thing I should say is that based on different people's experience on these forums some switches revert to flooding without an IGMP querier, whether that be PIM or an IGMP snooping querier which ties in with what I thought happened but some people have reported that without a querier but with IGMP snooping enabled the switch simply doesn't forward the multicast.

It seems to be platform dependant.

Jon

[jacnetoanbima]

"The switch will not change the multicast mac address to a broadcast mac address but it will simply flood the multicast to all ports in the vlan (other than the one it was received on)." But with wireshark, in the same vlan of multicast applications, I don't receive multicast traffic. Only interfaces with multicast aplications receive the multicast traffic and there aren't multicast mac in cam table.