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Date: Tue, 17 Mar 2009 15:54:42 +0100
From: Paolo Pisati <p.pisati@oltrelinux.com>
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To: Alex Dupre <ale@FreeBSD.org>
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Cc: freebsd-ipfw@freebsd.org, Dmitriy Demidov <dima_bsd@inbox.lv>,
	Luigi Rizzo <rizzo@iet.unipi.it>
Subject: Re: keep-state rules inadequately handles big UDP packets
 or	fragmented IP packets?
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Alex Dupre wrote:
> Luigi Rizzo ha scritto:
>> it is not related to dynamic rules, but to the fact that
>> that the firewall is called before reassembling packets.
>> The info (port numbers especially) is not available
>> in the fragments so the firewall cannot do anything.
>> The only solution would be to call the firewall
>> after reassembly. I am not sure if there is any work in progress
>> for that.
>
> FWIW pf has "traffic normalization" feature ("scrub" keyword), that 
> reassembles packets before inspection. Unfortunately, it works with 
> IPv4 packets, but lacks IPv6 support.
>
FYI i have a patch for ipfw nat that reassemble a packet before nat[*], 
but if the idea of an explicit packet reassembly action sounds good, i 
could move the code over there.

[*] actually the patch is really simple, it's just a call to ip_reass() 
with some glue code, but nonetheless it could be used more globally.

-- 

bye,
P.