problem with Demos/sockets/mcast.py

[Charles Follett]

Whenever I attempt to select a multicast group, like when running
mcast.py, I get:

  File "mcast.py", line 89, in openmcastsock
    s.setsockopt(IPPROTO_IP, IP_ADD_MEMBERSHIP, mreq)
socket.error: (22, 'Invalid argument')

Multicast works on my machine, and 'mcast.py -s' sends just fine
(verified with a sniffer.) What is preventing me from listening? Also,
I have two ethernet interfaces on my machine, and I was wondering how
to manually choose what interface is used. Thanks in advanced.

charley