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From: Wojciech Puchar <wojtek@wojtek.tensor.gdynia.pl>
To: Mario Lobo <mario.lobo@ipad.com.br>
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Cc: freebsd-questions@freebsd.org
Subject: Re: [OT?] tcpdump overhead
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>
> I am writing a final paper for a PG course and  I need to take precise
> measurements on network performance. I gonna be doing lots of packet dumps
> and I would like to know you guys' opinion on how much of tcpdump overhead
> (if meaningful for these measurements) I should take into account.
>
> If there are any readings on the subject you could point me to...

no idea but small for sure. it would rather cause tcpdump to not catch all 
packets that network performance drop.