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From Stefan Viljoen <>
Subject [NET] FTP - How to connect through a challenge / response firewall sequence
Date Sun, 27 Nov 2005 08:11:56 GMT
Hi guys

I have to write a FTP app that does the above - the app works perfectly 
outside the target network's firewall, but from behind it is a mess.

The procedure used on a FTP commandline inside the firewall is to specify the 
target machine outside the firewall by doing

1. ftp
2. The firewall comes back and asks for a firewall username and password, 
which the user provides in the terminal in the format 
localusername@firewallusername@remoteftpmachine. The firewall then prompts 
for a password, which is provided in the form 
remote_machine_password@firewall_password   The firewall responds with a 

331 Account Unit:  netscapewww1
331 -

3. Only after doing this is the remote FTP connection made.

The "firewall" FTP server identifies itself as "Check Point Firewall-1 Secure 
FTP server running on fw"

How can I accomodate this challenge / response cycle into my FTP app using Currently, it is impossible for my FTP application to connect 
from behind this firewall, since it does not execute the above challenge / 
response sequence, and the firewall then appropriately ignores the socket 
request to establish the FTP connection to the machine outside the firewall 
causing an IOException.

ANY help or pointers appreciated!

Stefan Viljoen
Software Support Technician / Programmer
Polar Design Solutions

Mobile: (+27) 83 4060854
Tel: (+27) 18 297 1753
Fax: (+27) 18 290 5556

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