National Aeronautics and Space Administration

FTP CONNECTION PROBLEMS

Some users have reported problems when downloading files from our web site
using FTP.  In a few isolated cases this is because the user's IP address
has been inadvertently blocked by NASA's spam filtering software.  If this
is the case you will not get any response at all from the HEASARC ftp
server.   More typically, however, the user will see a login message, and
then a message similar to "Service not available, remote server has closed
connection".  We are not exactly sure of the cause of this problem, but it
appears to occur only when the user's machine is located behind a firewall
which has not been set up properly to allow FTP access.  FTP data transfer
does not come back on the same port that the original connection is made on,
so unless the firewall is configured to recognize the FTP replies, it will
think that it is a new connection and will block it.  Stateful firewalls see
outgoing connections and can keep track of replies. If you have this
problem, you need to talk to your system administrator about changing the
configuration for your firewall or FTP software.

Fortunately, HTTP connections do not have this problem, so as a work around
users can download our files using HTTP rather than FTP. To do this, note
the FTP address that is causing the problem, and then modify the address by
substituting "http://" instead of "ftp://", and inserting the string "/FTP"
after the ".gov" in our machine address.  For example, the following FTP
address

   ftp://heasarc.gsfc.nasa.gov/fits_info/sample_files/events/

should be changed to:

   http://heasarc.gsfc.nasa.gov/FTP/fits_info/sample_files/events/

Enter this http address in your web browser to download the file.

Web page maintained by: Bryan K. Irby