IGMP and IGMP snooping both are different protocol. IGMP is used between host and multicast router for multicast membership communication and IGMP snooping is used on switch /vlan to limit forwarding multicast traffic to only interested host on switch.
Behavior on Cat4948/15.0(2)SG5
1) show ip igmp groups ----output for v2 and version 3 only if pim sparse mode is configured under the interface at layer 3.
2) Show ip igmp membership ---output for version 3. version 3 needs to be configured.
3) show ip igmp snooping groups --------output for v2 and version 3.
4) Show ip gimp snooping membership- No output at all even with multiple images. Explicit tracking must be enabled for output for command 4 .
5) Scenario -1 : If igmp snooping is disabled, it will flood the traffic . Enabling of igmp at layer 3 interface like pim -sparse mode does not affect.
6) Scenario -2 : If igmp snooping is enabled and there is no entry in the snooping table for particular multicast group, it will not flood the traffic and looks like it is get dropped.
7) show ip gimp snooping mrouter
8) show ip gimp snooping querier.
Note: In source only vlan, traffic is only forwarded to mrouter port if igmp snooping is enabled.
Note : Whenever we configure the igmp version 3, host on the LAN automatically switches to version 3 and start sending version 3 membership report. And when we unconfigure , it switches back to igmp version 2.
Note: Enable igmp querier on same vlan switch if there is no querier.
Behavior on 6500
Note : On cat6k , show ip igmp snooping groups does not work and need to use the "show mac address-table address multicast igmp-snooping" since forwarding is based on the layer 2 mac-address.
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