From owner-freebsd-net@freebsd.org  Tue Aug 25 22:54:04 2015
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Date: Tue, 25 Aug 2015 15:47:28 -0700
From: Chris Stankevitz <chris@stankevitz.com>
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Subject: ssh over WAN: TCP window too small
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Hi,

# cat /dev/urandom | ssh root@host 'cat > /dev/null'

I use the above ssh command over a high-BDP WAN link (80 ms @ 100 Mbps). 
  tcpdump shows I am TCP window limited to 64 KBytes (yielding 5 Mbps). 
  iperf with default options gets the window opened to 500 KBytes 
(yielding 35 Mbps).

Both sides of the connection: FreeBSD 10.1 w/default sshd options 
(except I permit root login).  In particular, HPN is not disabled.

Can anyone explain my abysmally small TCP window?

Can anyone recommend some tools/tricks to figure out what in FreeBSD 
and/or base SSH is limiting the send/recv buffer and/or TCP window?

Thank you,

Chris