I am looking for a good simple tool that runs on a standard OS (Windows or Linux) that I can used to test that multicast is being passed properly by a router.

I have been asked by a client to enable multicast routing on a Linux box acting as their router since their phone system requires multicast to for a few features. Since I am not physically near the client I don't really have the ability to experiment with the various methods for setting up multicast routing on Linux. I can setup a router at my desk that is identical to what is deployed on their network, but I don't know of any good simple tools that I can use to generate or listen for multicast traffic.

The one mulicast tool I have found is mcast.exe tool which is part of the Windows 2000/2003 resource kit. From what I have read online it seems that mcast.exe does not work across a router, and only works on the local network, so that doesn't seem to be useful for me to test multicast routing.

So what do tool(s) do you use to test that multicast routing is properly setup?