Just found this "gem" in the JDK bug database:
"The JDK requires all sockets be IPv4 or all sockets be IPv6. It doesn't support
the scenario where some Sockets are IPv4 and others are IPv6"
http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6914801
This means as long as the agent is talking IPv4 to anyone, e.g. because on startup we give
the debugger attach flags,
it will not be able to make any IPv6 connection afterwards. Attempts to do so will result
in
" java.net.SocketException: Protocol family unavailable "
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