Hi Hussein,
You can see the multicast groups with show ip igmp snooping groups but it won’t show the corresponding MAC addresses that are used per group. About your questions:
You can use this if you expect packet loss on your subnet. It changes the interval for some IGMP messages. The downside of changing this is that you increase the leave latency:
- Group member interval: this is the amount of time that the router waits before it determines there are no members left in the group. It is calculated as (robustness variable * query-interval) + (1x query response interval).
- Other querier present interval: the amount of time that a router has to wait before determining there is no other multicast router that is the querier. Calculated as (robustness variable * query interval) + (0.5 x query response interval).
- Last member query count: number of group specific querier that the router sends before it determines there are no members left in the multicast group. The number of queries is equal to the value of the robustness variable.
The reason it can’t be zero is probably because of the last member query count. A setting of 0 would indicate it won’t send any last member query count messages.
That is a good question…I didn’t see this before but you are right, the output is exactly the same. Probably a Cisco IOS quirk…
Before Cisco IOS 12.1(11b)EW, the default behavior of the switch was to flood multicast traffic on all interfaces when it receives a TCN (which indicates a spanning-tree topology change). The idea behind this is that multicast traffic is not interrupted but it can get pretty ugly if you have a lot of multicast traffic which is why there is the no ip igmp snooping tcn flood command.
This command disables the flooding of multicast when a TCN is received, and you can set it per interface.
Hmm I think this depends on the platform and IOS version. I don’t believe there is a separate command to enable/disable IGMPv3 snooping.