Great Circle Associates Firewalls
(August 1995)
 

Indexed By Date: [Previous] [Next] Indexed By Thread: [Previous] [Next]

Subject: Netscape's FTP through a Firewall
From: clh @ ptech . com (Charles L. Hutson)
Date: Thu, 10 Aug 95 11:27:18 EDT
To: firewalls @ greatcircle . com

I'm having a problem using Netscape to FTP through my Firewall-1 firewall.
I've done quite a bit of testing and research and have figured out that
its because Netscape's version of ftp adheres to the specifications of
RFC 1579.  This RFC states that instead of doing a PORT command to tell
the ftp server what port to open a data connection on, it does a PASV
command.  The following quote is from the above RFC:

   Fortunately, the necessary mechanisms already exist in the protocol.
   If the client sends a PASV command, the server will do a passive TCP
   open on some random port, and inform the client of the port number.
   The client can then do an active open to establish the connection.

This is the part that confuses me.  If the server is going to inform
my client of the port number "on some random port", 1) How am I going
to know which port to listen on to get this critical information?  It
seems like my ftp client would have to be frantically scanning the
entire range above 1024 to get this information.   2) Isn't
this going to force me to leave the entire range above 1024 wide open
in my firewall configuration?

As it stands, I can't FTP through Netscape because my firewall blocks
that incomming random packet.  Can anyone provide any suggestions.

    _______________________________________  
   / ____  _____ _____                     \   Charles L. Hutson, clh @
 ptech .
 com
  / ____//  //  // ___  Technical Services  \  Systems Engineer
 / //      //  //___//       Division       /\ Piedmont Technology Group
/__________________________________________/ / Phone 704.523.2400
\__________________________________________\/  Fax   704.523.7764




Follow-Ups:
Indexed By Date Previous: Running ISDN links using PPP - where should they go ?
From: Danny Cox <dannyc @ gmap . leeds . ac . uk>
Next: Re: SunOS vs Solaris 2 vs Intel/BSD for firewalls
From: peter @ nmti . com (Peter da Silva)
Indexed By Thread Previous: Running ISDN links using PPP - where should they go ?
From: Danny Cox <dannyc @ gmap . leeds . ac . uk>
Next: Re: Netscape's FTP through a Firewall
From: Nick Simicich <njs @ scifi . maid . com>

Google
 
Search Internet Search www.greatcircle.com