is sent an unknown command (not in the list above),
+it replys to the client "unknown_cmd".
+
+
+=item UNKNOWN CLIENT
+
+If the anti-spoofing algorithm cannot verify the client,
+the client is rejected (with a "refused" message sent
+to the client, and the connection is closed.
+
+=back
+
+=head1 PREREQUISITES
+
+IO::Socket
+IO::File
+Apache::File
+POSIX
+Crypt::IDEA
+LWP::UserAgent()
+GDBM_File
+Authen::Krb4
+Authen::Krb5
+
+=head1 COREQUISITES
+
+=head1 OSNAMES
+
+linux
+=head1 SCRIPT CATEGORIES
+Server/Process
+=cut
500 Internal Server Error
Internal Server Error
The server encountered an internal error or
misconfiguration and was unable to complete
your request.
Please contact the server administrator at
root@localhost to inform them of the time this error occurred,
and the actions you performed just before this error.
More information about this error may be available
in the server error log.