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
Symbol
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.