Re: ftp?

[Tech Support <support@elbnet.com>]

Marc-Adrian Napoli wrote:
> 
> hi,
> 
> have a wierd problem here. we have standard debian box here running wuftp,
> as well as an NT box with iis 5.0. (and ftp)
> 
> a particular customer sitting behind a NAT'd firewall cant connect to our
> debian wuftp server, but has no problem with the NT box.
> 
> ive allowed their specific class C range access in hosts.allow and i can ftp
> into the box with their account no problems.
> 
> the customer gets an FTP connection but no prompt for username and password,
> has anyone seen this before?
> 

   This is a fairly common problem with trying to run FTP through a
firewall. FTP creates two connections: an outbound connection and a
return connection. 

  The outbound conection is easy: from the clients unprivledged ports to
the server port 21 and back.
 The return connection is a problem. You have to allow *anyone* to
connect to your port 20.

  The reason that you do not get a login prompt is that the firewall is
rejecting the inbound connection.

 Often you can get around this problem by using passive mode FTP (which
is probably why they can connect to the M$ box) which connects to one of
your unprivledged ports instead of 20.

Another way around the problem if your client doesn't want to mess with
their firewall is to offer HTTP based FTP.

Pete