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Date: Mon, 9 Jan 2012 14:47:25 +0100
From: Corinna Vinschen <corinna-cygwin AT cygwin DOT com>
To: cygwin AT cygwin DOT com
Subject: Re: Cygiwn's sshd, 2 tunnels and file transfer fails
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On Jan  6 14:42, Michael Wiedmann wrote:
> Given the following test scenario:
> 
>  +-----------+         +-----------------+           +-----------+
>  | Client #1 |         |  Server (XP/7)  |           | Client #2 |
>  | - ssh     |   1)    |   Cygwin/sshd   |   2), 3)  | - ssh     |
>  | - httpd   +-------->+                 +<----------+           |
>  +-----------+         |                 |           +-----------+    
>                        +-----------------+
> 
> 1) client #1 initiates a ssh connection to cygwin/sshd _and_
>    requests "remote port forwarding" like:
>    -R 60000:client_#1_ip:80 server_ip
> 
>    This works w/o any problems
> 
> 2) client #2 initiates a ssh connection to cygwin/sshd _and_
>    requests "local port forwarding" like:
>    -L 1234:127.0.0.1:60000 server_ip
>    
>    This works w/o any problems
> 
> 3) client #2 accesses httpd on client #1 using 127.0.0.1:1234
> 
>    This works for "simple" web browsing
> 
>    But if client #2 tries to upload "large" files, e.g. like:
> 
>    curl -X PUT -d @file.txt http://127.0.0.1:1234/uploaddir/file.txt
> 
>    to client #1's httpd this fails after transferring only a small
>    part of the file.

How does it fail?

>    The ssh connection itself is not affected and stays intact.
> 
>    It looks like the TCP congestion/overload control mechanism of the 
>    two TP streams does not work properly in this case.

Cygwin is not the OS and it doesn't implement it's own TCP stack
so there's no congestion control or something comparable.


Corinna

-- 
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Project Co-Leader          cygwin AT cygwin DOT com
Red Hat

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