Best utilizing fat long pipes and large file transfer

Date: Fri, 13 Jun 2008 09:02:31 +0900
From: Randy Bush <>

> 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