Re: [Qemu-devel] Connecting vde and LAN

[Oliver Gerlich <olig9@gmx.de>]

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Henrik Nordstrom schrieb:
> On Sun, 10 Jul 2005, Oliver Gerlich wrote:
> 
>> what is the best solution to connect the vde "switch" to my real LAN so
>> that Qemu guests get IPs from my LAN-wide DHCP server?
> 
> 
> bridgeing of your ethernet interface and the TAP interface connecting to
> vde is undoubtly the best if you want to provide full access to the LAN.
> 
>> So far I've experimented with bridging tap0 and eth0 so that the Qemu
>> guests are transparently on my LAN and get IPs from the LAN-wide DHCP
>> server. But this has the drawback that my host network interface is now
>> br0 instead of eth0 (that causes confusion at least for samba).
> 
> 
> Fix the Samba problem?
> 
> Why does this cause problems for Samba? I run my qemu stations like this
> all the time, but not using Samba..

The "problem" is that I start vde_switch and the bridging not at boot,
but when I want to run Qemu. So then I have to restart Samba to bind to
to br0 instead of eth0. Not so much of a problem though... Only I don't
know what other services already rely on eth0 as my network interface :)

Could you explain how you integrated vde_switch and bridging with your
current system? Do you start everything at boot and accept that this
changes the system-wide network configuration, or do you use some
bridging trick to avoid this?

> 
>> Also I tried to set up IP forwarding between tap0 and eth0, but then the
>> Qemu guests aren't transparently on my LAN (and don't get the correct
>> config from the DHCP server).
> 
> 
> Correct.
> 
> DHCP is Ethernet broadcast based, not IP.
> 
> You could in theory run a DHCP proxy agent on your tap0 interface, and
> have the DHCP server configured with a suitable scope. But this does not
> give you addresses from your LAN.
> 
> You could also run a local DHCP server on tap0, configured with the
> address scope you have set up proxy-arp for. But these addresses better
> be statically assigned to you, never handed out by the LAN DHCP server
> to anyone else in the LAN. But this doesn't provide true LAN access,
> only routed acces to the LAN (no broadcasts).

So it looks indeed that vde and bridging is the way to go.
Thanks for your explanations :)

> 
> Regards
> Henrik
> 
> 
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> 
> 

Greetings,
Oliver
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