netdev - Re: RFC: Established connections hash function

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Date:	Fri, 23 Mar 2007 09:17:19 +0100
From:	Eric Dumazet <dada1@...mosbay.com>
To:	Evgeniy Polyakov <johnpol@....mipt.ru>
Cc:	David Miller <davem@...emloft.net>, nikb@...master.com,
	netdev@...r.kernel.org
Subject: Re: RFC: Established connections hash function

Evgeniy Polyakov a ecrit :
> Call me a loooser which mail will be deleted on arrival, but...
> 
> jhash_2words(const, const, ((const << 16) | $sport) ^ $random)
> 
> where $sport is 1-65535 in a loop, and $random is pseudo-random number
> obtained on start.
> 
> Which is exactly the case of web server and attacker connects to 80 port
> from the same IP address and different source ports.
> 
> Result with jenkins:
> 1 23880
> 2 12108
> 3 4040
> 4 1019
> 5 200
> 6 30
> 7 8
> 8 1
> 
> Xor:
> 1 65536

So what ? You still think hash function must be bijective ? Come on !

You have a machine somewhere that allows 65536 concurrent connections coming 
from the same IP address ?

The last problem you have is the nature of tcp hash function.

Dont argue again with your pseudo science.

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