A 'client' is a 'client application' - you can broadcast messages wherever you like, but unless something's listening and acting on those messages, they're not a lot of good. You can't just send a message to a machine and expect it to magically do something...what were you expecting, exactly? mcast_send(PopupWindow=>1,PlaySound=>"ding.wav")? Anything that causes the client to take action must aleady be running on the client machine.

Two paragraphs down fom the IO::Socket::Multicast synopsis you've pasted in there, it explains how to write a multicast client that will listen to your multicast server. That should get you started, if this is what you need.

Cheers, Ben.