Extensions for long fat networks?

Paul Hyder paul.hyder at noaa.gov
Sat Jun 14 09:37:27 EST 2003

Damien Miller wrote:
> Paul Hyder wrote:
> > Before I get too far in my attempts...
> >
> > Has anyone already implemented support in scp for larger
> > buffers/windows that would take advantage of wscaled TCP
> > windows?
> Shouldn't this be done at the system level? That way all apps would benefit.
> IIRC Linux has something in /proc that one may tweak.
> -d

(Believe this is also what the previous message from Frank was noting.)

Tuning TCP in Linux 2.4.18+ is actually easy and has good documentation.
(/proc/sys/net/core/[rw]mem_{max,default} and /proc/sys/net/ipv4/tcp_[rw]mem)
So getting wscaled connections was fast.

What I've found so far is that ssh has an internal idea of transmission
and the result is that the underlying large TCP windows are under-utilized.
The answer also doesn't appear to be as easy as increasing
CHAN_TCP_PACKET_DEFAULT above (32*1024).  [But I've just started and
could easily have missed something.]

With encryption requirements and lots of LFN availability I was just
hoping someone else had already run into the low long distance
throughput and fixed it.

Any/all further suggestions and recommendations would be appreciated.
(Particularly the ones that start with "Whatever you do, don't...")
	Paul Hyder
	NOAA Forecast Systems Lab
	Boulder, CO

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