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Why does server unexpectedly dropped the connection only from a specific location?

Posted on 2011-03-14
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Last Modified: 2013-12-09
Hello,

my company has got a private ftp server in our office in the US, it's set up with Rumpus and it's accessible via HTTP on a web browser on a public IP address.
I can access it without any problem on every internet connection i tried, except from one of our European offices. This office has got 2 connections, one XDSL on which the FTP access via HTTP is working fine and another one, ADSL on which is the problem :

Every time I try to connect (and i tried from several machines) :
- Firefox leaves me on a blank page
- Chrome tells me : The webpage at http://www.XXX.com/ might be temporarily down or it may have moved permanently to a new web address.
Error 324 (net::ERR_EMPTY_RESPONSE): Unknown error.
- Safari tells me : Safari can’t open the page “http://www.XXX.com/” because the server unexpectedly dropped the connection. This sometimes occurs when the server is busy. Wait for a few minutes, and then try again.

Where could the problem come from and what can i do???
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Question by:bafforosso
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Expert Comment

by:TomRScott
ID: 35130323
Some diagnostics to consider:
Can you ping the server over the ADSL link?
Have you tried to Telnet an FTP session with the server?

Assuming you are using HTTPS for your FTP sessions, is HTTPS allowed over the ADSL link?

If you are using two firewalls, the rules may be different between them. Try a "stare and compair" of the firewall rules between the two firewalls. If using a single firewall but with two external ports for the XDSL and ADSL links stare and compare the rules for the two ports. If you are using a SonicWALL the two ports are NORMALLY in the same "zone" and this should not be a problem (cause), in that case.

These are initial ideas.

 - Tom
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Author Comment

by:bafforosso
ID: 35136161
Hi,

thanks for the advice.

Yes i can ping the server without packet loss.

I can reach the server when I Telnet an FTP session but it'll keep telling me Login Failed, even when my login and password are the right ones.
We are using a SonicWALL for the XDSL link and a built-in on a Thompson modem-router for the ADSL one, but i tried disabling it completely and it doesn't change anything, could it be a problem on the ISP side?
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Expert Comment

by:TomRScott
ID: 35136313
Some ISPs block various traffic (some even FTP) for various reasons. However, that should block the entire session and not cause the credentials to fail.

Just to compare apples to apples as much as possible, are you able to use Telnet to FTP to the server via the "good" Internet connection? If not, we need to do so. It could be that your server is configured in such a way as to make this test invalid for your situation.

If both fail using Telnet, are the failure messages the same?

 - Tom
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Accepted Solution

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AlexPace earned 125 total points
ID: 35157644
To really figure out what is happening you'll need to use a client with the ability to create an FTP protocol-level log file so you can see exactly which raw commands are being sent to the server and how the server replies.

Robo-FTP more of a development tool for creating scripts that do repetitive upload tasks but it has nice logging and a 30-day eval that you could use to at least get a handle on the issue.  After installing it, type these commands into the console window:  (use server ip, username and password)
TRACELOG "problem_trace.log"
FTPLOGON "192.168.XXX.XXX" /user="MyUserID" /pw="MySecret" 
FTPLIST
FTPLOGOFF 

Open in new window

This should cause Robo-FTP to attempt to connect to your FTP server get a directory listing of the root folder.  It will create a log file of everything that it sends to the server and all of the server's replies.

Look under the Robo-FTP installation folder and find a new file named problem_trace.log and it will show the actual low-level raw FTP conversation between the client and the server.  Please post that file so we can help troubleshoot.
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Author Comment

by:bafforosso
ID: 35178568
Hello,

i solved my problem, thanks AlexPace, it helped me a lot. I found that my predecessor had set up heuristic blacklist layer ahead of the ftp server to prevent Rumpus' last resort solution, "disable account". And at a certain point it blacklisted our European office IP.
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