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Date: Sun, 28 Sep 2003 12:40:32 -0400 (EDT)
From: Robert Watson <rwatson@freebsd.org>
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To: Dambielle Yannick <yannick.dambielle@free.fr>
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Subject: Re: tcpdump - tun/tap virtual interfaces
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On Sun, 28 Sep 2003, Dambielle Yannick wrote:

> I've tried to dump some paquets sent to a virtual interface without any
> success for a couple of hours so I ask for some helps to the list.  I
> use a FreeBSD 5.0, my kernel has been rebuilt and installed with the
> following option in order to use a tap virtual interface : device tap
> The virtual interface has been created (tap0) and I've attached the IP
> adress 10.0.0.1. It seems ok, I can see it with ifconfig.  All the tests
> are local tests.  While I ping 10.0.0.1 (paquets are sent and not lost),
> I laught a tcpdump -i tap0 from another shell... Nothing is dumped
> (?!)...  Well, if some of you has an idea, I'll be very happy. 

Do you see anything when you ping the broadcast address or other foreign
address of the tap interface?  Packets delivered to local IP addresses
generally don't go out an interface. 

Robert N M Watson             FreeBSD Core Team, TrustedBSD Projects
robert@fledge.watson.org      Network Associates Laboratories