full-disclosure - Re: DNS and NAT (was: DNS and CheckPoint)

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Date: Fri, 11 Jul 2008 11:51:42 -0400
From: Valdis.Kletnieks@...edu
To: Thomas Cross <tcross@...ibm.com>
Cc: full-disclosure@...ts.grok.org.uk
Subject: Re: DNS and NAT (was: DNS and CheckPoint)

On Fri, 11 Jul 2008 11:01:33 EDT, Thomas Cross said:

>     Thanks for testing this. A number of other readers wrote me privately
> confirming your result with linux ipchains. I'm not sure what ipchains does
> when it encounters a collision, but in general I think this is a good
> strategy. You'd have to have many thousands of simultaneous UDP
> transactions in order for randomly selected source ports to be colliding
> frequently enough for it to present a substantial problem.

Birthday paradox strikes again.

With 64K source ports, you'll have collisions over 1% of the time at only 1024
in use. With 8K in use, you're hitting collisions 12% of the time.

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