Re: tcpdump on tap100: no packets shown, even though they arrive/get replied to

[Manuel Bouyer <bouyer%antioche.eu.org@localhost>]

On Wed, Aug 24, 2011 at 06:11:16PM +0100, Robert Swindells wrote:
> 
> What is tap3 for, and why isn't there a real ethernet device in this
> bridge ?

You don't have to have a real ethernet on a bridge. In a Xen context,
this means you have a ethernet network connecting domUs which doesn't
exists outside the physical box.

> >On OpenBSD, I see @ the arp cache table:
> >? (172.16.99.133) at f2:0b:a4:3c:ba:02 on em3
> >
> >And I'm logged in on machine A, through the IP assigned on tap100 there
> >(which is bridged via bridge3).
> 
> You don't want to assign an IP address to the tap device.

Why ? I've had IPs addigned to tap devices (for other reasons)
and it worked fine.

> >It works as expected, it's just that I can't see any packets to tap100,
> >and tcpdump doesn't work on bridges (it seems).
> 
> I have some local diffs to bridge(4) to add support for bpf.
> 
> The tap(4) device is intended for use by machine emulators, it isn't
> a general debug interface.

Not only machine emulators. It's also used by e.g. openvpn.

-- 
Manuel Bouyer <bouyer%antioche.eu.org@localhost>
     NetBSD: 26 ans d'experience feront toujours la difference
--