Best utilizing fat long pipes and large file transfer

Kevin Oberman oberman at
Fri Jun 13 02:11:06 UTC 2008

> Date: Fri, 13 Jun 2008 09:02:31 +0900
> From: Randy Bush <randy at>
> > The idea is to use tuned proxies that are close to the source and
> > destination and are optimized for the delay. Local systems can move data
> > through them without dealing with the need to tune for the
> > delay-bandwidth product. Note that this "man in the middle" may not
> > play well with many security controls which deliberately try to prevent
> > it, so you still may need some adjustments.
> and for those of us who are addicted to simple rsync, or whatever over
> ssh, you should be aware of the really bad openssh windowing issue.

Actually, OpenSSH has a number of issues that restrict performance. Read
about them at <>

Pittsburgh Supercomputer Center fixed these problems and on FreeBSD, you
can get these by replacing the base OpenSSH with the openssh-portable
port and select the HPN (High Performance Networking) and OVERWRITE_BASE
options. I assume other OSes can deal with this or you can get the
patches directly from:

The port may also be built to support SmartCards which we require for
R. Kevin Oberman, Network Engineer
Energy Sciences Network (ESnet)
Ernest O. Lawrence Berkeley National Laboratory (Berkeley Lab)
E-mail: oberman at			Phone: +1 510 486-8634
Key fingerprint:059B 2DDF 031C 9BA3 14A4  EADA 927D EBB3 987B 3751
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