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Re: ssh-vs-rsh benchmark result

On Fri, 30 Aug 2002 09:46:46 -0400
Adam C Powell IV <hazelsct@mit.edu> wrote:

> So clearly, ssh connections take longer to start.

There is probably a misunderstanding on how ssh works.

ssh uses two different encryption mechanisms, one is 
public-key encryption, and second is the usual shared key encryption.

public-key encryption is used to encrypt the shared key and 
send it to the other end. This process is known to be costly and 
slow. After that negotiation phase, we move over to shared key

Another thing is, us Beowulf users may use ssh to start up 
processes, but we usually use pvm/mpi etc. processes.
We usually don't communicate through stdin/stdout/stderr.

mpi etc. use standard TCP/IP communication channels, which
are unencrypted.

ssh only encrypts what is sent through stdin/stdout.
(and other things that explicitly use ssh tunnel, which
mpi doesn't, AFAIK)

Corrections welcome.


dancer@debian.org  http://www.netfort.gr.jp/~dancer

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