Chris Stankevitz wrote:
Hi,
# cat /dev/urandom | ssh root at 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?
I know this response is a little late to the party, but...
I spent a bit of time last year tuning my FreeBSD 10.1 host to be
able to transfer a bunch of data between the east coast of the US
and the west cost. My WAN link was more like 70ms @ 75 Mbps, so
not too different than yours. The other end of the connection was
also a FreeBSD 10.1 host.
I have the following in my /etc/sysctl.conf - and I get pretty much
all 75Mbps when I scp or rsync a file:
# tcp options for long-haul speedups
kern.ipc.maxsockbuf=4194304 # (2 * default 2097152)
net.inet.tcp.mssdflt=1448 # (default 576)
net.inet.tcp.sendbuf_max=4194304 # (2 * default 2097152)
net.inet.tcp.recvbuf_max=4194304 # (2 * default 2097152)
net.inet.tcp.syncache.rexmtlimit=1 # (default 3)
net.inet.tcp.recvspace=262144 # (4 * default 65,536)
net.inet.tcp.sendspace=262144 # (4 * default 65,536)
net.inet.tcp.sendbuf_inc=65536 # (8 * default 8192)
net.inet.tcp.recvbuf_inc=131072 # (8 * default 16384)
One thing that was noticed - it can take a really, really, really
long time for the TCP window to open up the whole way with the
default net.inet.tcp.sendbuf_inc setting!
-Kurt
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