The initial question was "how to monitor the multicast Internet?", and
the answer is *hard* - you can't easily do it from just within one
network, as you never have a proper full view of multicast packets
flowing "to" and "fro".
Is there such a thing as "the multicast Internet"?
I've thought and talked about this before ...
The thing I was told is "nobody does IP multicast as bandwidth is cheap".
Apparently, people who need multicast-like features do it a few layers
higher on the OSI model.