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From: Andrew <granica_raydom@rambler.ru>
To: Max Laier <max@love2party.net>
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Cc: freebsd-net@freebsd.org
Subject: Re: ipv6 connection hash function wanted ...
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On Tue, 14 Nov 2006 17:09:20 +0100
  Max Laier <max@love2party.net> wrote:
> Hello,
> 
> this one is something for people who know their math.
> 
> Input: 2x128bit of address (lower ~80bit selectable by user) and 
>2x16bit 
> of ports (more or less selectable by user).  Note that the "flow_id" 
>is 
> not useable as several broken stack implementations do not set it 
> consistently - and it is user settable as well.
> Output: "int" hash value - by default we use the lower 8bit of it.
> 
> Problems: Most of the input can be selected by a user meaning it is 
>easy 
> to produce collisions.  For legal connections, the lower 64bit are 
>the 
> one with the highest entropy - in fact the upper 64bit might be the 
>same 
> for many connections coming from/going to the same subnet.  This 
>function 
> will be used for every packet that is passed to a dynamic IPFW rule, 
>so 
> efficiency is a concern.
> 
> Any ideas?  Any papers that deal with this problem?
> 
> ref: sys/netinet/ip_fw2.c::hash_packet6
> 
  May be the Rsync algorithm is suitable partially..

Here is the discription: http://samba.anu.edu.au/rsync/tech_report/

  Andrew.