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Re: Port Randomization: New revision of our IETF Internet-Draft
From: Fernando Gont <fernando.gont () gmail com>
Date: Sun, 07 Sep 2008 01:31:48 -0300

At 07:39 p.m. 03/09/2008, Jerome Benoit wrote:

We have published a revision of our IETF Internet-Draft about port
randomization.  It is available at:
http://www.gont.com.ar/drafts/port-randomization/draft-ietf-tsvwg-port-rand
omization-02.txt (you can find the document in other fancy formats at:
http://www.gont.com.ar/drafts/port-randomization/index.html)


Hi,

I'm still wondering how much overhead algorithm #3 and #4 add ...
Did someone have done some tests ?

This is a good point.

Well....in the case of algorithm #3, that depends on the hash 
function you use for F(). In the case of algorithm #4, that depends 
on the hash function you use for F() and the hash function you use for G().

FWIW, Linux implements algorithm #3, so you could measure the 
performance of that algorithm already.

P.S.: If you care about the performance implications, that's probably 
because you are issuing a large number of connection requests. In 
that case, algorithms #1 and #2 are probably not a choice, as they 
are likely to lead to a large number of connection-id collisions. 
And, if your connection requests are being issued to different hosts 
or services, algorithm #4 will have a better port reuse frequency 
that even the traditional BSD port selection algorithm, thus probably 
avoiding some collisions that you would have experienced with the 
traditional BSD port selection algorithm.

Thanks!

Kind regards,

--
Fernando Gont
e-mail: fernando () gont com ar || fgont () acm org
PGP Fingerprint: 7809 84F5 322E 45C7 F1C9 3945 96EE A9EF D076 FFF1




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