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Date:      Wed, 19 Feb 2003 09:37:23 -0800
From:      Lars Eggert <larse@ISI.EDU>
To:        Audsin <dev.dhas@kcl.ac.uk>
Cc:        freebsd-hackers@freebsd.org
Subject:   Re: Packet length 1284 instead of 1280
Message-ID:  <3E53C0D3.70203@isi.edu>
In-Reply-To: <5.2.0.9.0.20030219133537.070e0c78@pop2.kcl.ac.uk>
References:  <5.2.0.9.0.20030219133537.070e0c78@pop2.kcl.ac.uk>
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[-- Attachment #1 --]
Audsin wrote:
> Sir / Madam
> 
> I am doing my research on fragmentation avoidance technique for mip6. I 
> am using FreeBSD4.4 with kame snap and ethereal to capture packets
> 
> I have a query regarding the packet length
> 
> If i am correct ,
>  packet length = IPHdr +extHdr+TCPHdr+TCPOpt+Data
> 
>                      =IPHdr+Routing Header + Frag Header + TCP Header+ 
> Tcpopt+ Data
> 
>                          40+24+8+20+12+1176=1280 (Which is the MTU of 
> the gif0 interface)
> 
> But my ethereal capture says the packet length to be 1284 btyes. Can 
> anyone please let me know what that 4 bytes is accounted for?

Can't help you with your question, but if you're using 4.4-RELEASE, the 
KAME -SNAP you're using must be ancient. There have been many fixes, 
especially to the MIP6 code, so upgrading to a recent -SNAP may simply 
make the problem go away.

Lars
-- 
Lars Eggert <larse@isi.edu>           USC Information Sciences Institute

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