[Bug 1697] scp transfers from remote cygwin machine fail with ssh versions >= 4.6

[bugzilla-daemon at bugzilla.mindrot.org]

https://bugzilla.mindrot.org/show_bug.cgi?id=1697

Charles Davis <cdavis at ingenuous.net> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |FIXED

--- Comment #2 from Charles Davis <cdavis at ingenuous.net> 2010-01-14 01:23:56 EST ---
(In reply to comment #1)
> I suspect you have a device in your network path that cannot handle
> large TCP windows, probably window scaling.
> 
> One of the changes in the 4.7 release was:
> 
>  * The SSH channel window size has been increased, and both ssh(1)
>    sshd(8) now send window updates more aggressively. These improves
>    performance on high-BDP (Bandwidth Delay Product) networks.
> 
> Previously this was limited to 64k, which is not enough to exercise TCP
> window scaling.  You can confirm this by looking at the "SendQ" field
> in the connection in the netstat output on the sending side (this is on
> Linux, I don't know how to get the equivalent data on Windows).  If the
> number is non-zero and doesn't decrease this is almost certainly the
> problem.
> 
> You can also try disabling window scaling.  On Linux, that's "echo 0
> >/proc/sys/net/ipv4/tcp_window_scaling".  I don't know about Windows
> but presumably it's in the registry somewhere.   You'll only need to
> disable it on one end and retry the copy.

This:
 "echo 0 >/proc/sys/net/ipv4/tcp_window_scaling"
completely fixes the problem. Thanks loads. 

As far as I am concerned it is fixed. So I am changing the status.

However, before I came to you fellows, I searched extensively and there
seems to ba a lot of instances of this problem. Is there somewhere I
can add a FAQ or soemthing like that??
Charles Davis

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