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Subject:	Cygiwn's sshd, 2 tunnels and file transfer fails
Date:	Fri, 6 Jan 2012 14:42:26 +0100
Message-ID:	<F5F6578C2B51B1469FE9A7A17315C8B7028D6F86@bermail01.de.aastra.com>
From:	"Michael Wiedmann" <michael DOT wiedmann AT aastra DOT com>
To:	<cygwin AT cygwin DOT com>
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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.

   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.

Testing the same scenario using a Linux sshd this works w/o any
problems.

Is this a known problem of Cygwin?

Any known workaround?


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