QEMU and tap problems

Doug Poland doug at polands.org
Fri Sep 21 05:08:46 PDT 2007


On Thu, September 20, 2007 20:47, RW wrote:
> On Thu, 20 Sep 2007 06:21:20 -0500
> Doug Poland <doug at polands.org> wrote:
>>
>> I've been following the various instructions I've found on the web
>> in an attempt to get tap networking with qemu-devel-0.9.0s.20070802
>>
>
> Are you actually sure that you actually need tap?
>
Good question.  My reason for running Win2K server under QEMU is I'm
working on a java app that speaks to SQLServer.  Initially, all I need
is to communicate with the host/guest on the same machine.  After
that, I'll need the QEMU guest to be on the network so I can connect
to the java app from other computers.

>
> A lot of the how-tos are out of date
>
I've noticed that :(

>
> - recent versions of Qemu can give a guest network access without it.
>
When I started QEMU with the -net nic -net user switches, then Windows
gets a 10. address and the guest can see the network.  However, I
cannot see open ports I'm interested in, 1433 and 3389, from the host.


>> Windows thinks it has connectivity, but I cannot ping the default
>> gateway from the guest and I cannot ping the IP of the guest from
>> the host.
>
> This suggest you are accessing the net without tap, ping is a setuid
> binary so pings generated in the guest can't be passed on by qemu.
>
The guest definitely could not see the hosts network with tap set up
the way I described.  I was using ping as a basic diagnostic tool and
did not know the limitation you described.


--
Regards,
Doug



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