IT ...

iperf can be used to test multicast traffic.

For future searchers, here is the recipe for "opening" a Foundry EdgeIron 48G:

In the web based interface, go to
IGMP Snooping --> IGMP Configuration -->
once there, uncheck IGMP Status and Ganglia should start receiving it's
info after one or two refreshes.

-Jeremy Lawrence

Same problem for 3Com switches.