tap interface problem

[Sébastien Serre]

On Sunday 27 September 2009 18:17:22 Sébastien Serre wrote:
> Hello, I hope somebody here known well tap interfaces on freebsd :).
> 
> I try to configure virtualbox with bridge interface. Everything seams ok:
> # ifconfig tap0
> 
> tap0: flags=8943<UP,BROADCAST,RUNNING,PROMISC,SIMPLEX,MULTICAST> metric 0
>  mtu 1500
>         ether 00:bd:4f:0a:00:00
>         inet 192.168.0.1 netmask 0xffffff00 broadcast 192.168.0.255
> 
> # ls -l /dev/tap0
> crw-rw-rw-  1 root  wheel    0, 109 Sep 27 16:54 /dev/tap0
> 
> The problem is that nothing pass in the tap0 interface. tcpdump does not
>  show any traffic when I try to connect a machine on the 192.168 network. I
>  can ping the interface address (192.168.0.1). But without with the use of
>  the tap itself (use of lo0):
> 
> # route -n get 192.168.0.1
>    route to: 192.168.0.1
> destination: 192.168.0.1
>   interface: lo0
>       flags: <UP,HOST,DONE,LLINFO,WASCLONED,LOCAL>
>  recvpipe  sendpipe  ssthresh  rtt,msec    rttvar  hopcount      mtu
> expire
>        0         0         0         0         0         0     16384       
>   0
> 
> 
> Then i have a tap interface up, but i can't pass to it any traffic.
> Does anybody have a suggestion, or know some debugging tools to show what
> append?
> 
> Thanks
> 
> Sebovick
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Me again,

I can now listen something on tap0:

# tcpdump -i tap0
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on tap0, link-type EN10MB (Ethernet), capture size 96 bytes
21:08:22.668835 arp who-has 192.168.0.1 tell 192.168.0.101
21:08:23.668526 arp who-has 192.168.0.1 tell 192.168.0.101
21:08:24.668272 arp who-has 192.168.0.1 tell 192.168.0.101
21:08:25.671499 arp who-has 192.168.0.1 tell 192.168.0.101

192.168.0.101 is my virtual machine trying to ping the host address of the tap 
interface. The host did not reply.
When I try to ping the guest from the host, tcpdump stay silent.

So the tap interface is ok for the guest, but the host don't know how to talk 
against tap. Any idea?