[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

Darren Tucker <dtucker at zip.com.au> changed:

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                 CC|                            |dtucker at zip.com.au

--- Comment #1 from Darren Tucker <dtucker at zip.com.au> 2010-01-13 22:25:50 EST ---
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.

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