From owner-freebsd-security@FreeBSD.ORG  Wed Dec 14 00:16:06 2005
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From: Darren Reed <avalon@caligula.anu.edu.au>
Message-Id: <200512140016.jBE0G9T4021056@caligula.anu.edu.au>
To: borjamar@sarenet.es (Borja Marcos)
Date: Wed, 14 Dec 2005 11:16:09 +1100 (Australia/ACT)
In-Reply-To: <A20DB37F-36A2-42D1-8B05-EC14EE0858A1@sarenet.es> from "Borja
	Marcos" at Dec 13, 2005 04:59:54 PM
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Cc: freebsd-security@freebsd.org
Subject: Re: Useful addition to ipfw
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In some mail from Borja Marcos, sie said:
> 
> 
> Hello,
> 
> I've found myself in a situation where a simple data inspection  
> capability added to ipfw would be very useful.
> 
> I'm not thinking about anything especially sophisticated, but what  
> about adding an option to check byte values (or flags, similar to  
> tcpdump)?
> 
> An example rule could be: add deny udp from any to me 12345 udp[4]&234
> 
> being the rule true if byte 4 in the UDP packet AND the number 234 is  
> not zero.

I believe you could do that today, with IPFilter, if you expressed
the entire packet-matching part of the rule with BPF.

Darren