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Date:      Thu, 16 Jul 2009 12:22:32 -0700
From:      Chuck Swiger <>
To:        Dmitriy Demidov <>
Subject:   Re: ipfw nat and localy initiated UDP traffic (bad udp cksum)
Message-ID:  <>
In-Reply-To: <>
References:  <> <>

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On Jul 16, 2009, at 12:19 PM, Dmitriy Demidov wrote:
> Update about this issue.
> There is somthing wrong with UDP pass through - ipfw nat makes it  
> "bad cksum".

tcpdump receives local network traffic before the checksums are  
computed (especially if hardware checksums are enabled); this is a non- 
issue, although you could confirm by sniffing the traffic from an  
external machine like a laptop.


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