Re: [Qemu-devel] Connecting vde and LAN

[Henrik Nordstrom]

On Thu, 11 Aug 2005, Oliver Gerlich wrote:

> Couldn't we avoid these incompatibilities if we would route packets only on 
> the Ethernet level? If the Qemu networking setup on the host involves IP 
> addresses or such things, we're already on the wrong OSI layer I think...

> From what I can tell there is no way userspace can send Ethernet frames to 
the host as if coming from the eth0 interface, short of writing a kernel 
module to make this magics happen.

> I'm not very experienced in networking, but IMHO the network should be set up 
> like this:
>
>                                    (eth0 on Host OS)
>                                   /
> ( LAN ) <----> (real eth0) <-> VDE
>                                   \
>                                    (NIC on Guest OS)

This is what you do with bridgeing.

                         (br0 on Host OS)
                         /
( LAN ) <---> eth0 <-> bridge
                         \
                         (tap0 to VDE/qemu)


Hmm.. actually the bridge setup can be simplified somewhat on Linux hosts 
by using an early boot script run before the eth0 is initialized, renaming 
eth0 to something else and creating a bridge named eth0, including the 
renamed eth0 interface..


   modprobe eth0
   ip link set eth0 name eth0real
   brctl addbr eth0
   brctl addif eth0 eth0real
   ip link set eth0real up


> So this is a summary of what I think we should try to achieve (sorted by 
> priority):
>
> -provide Ethernet-layer access from the Guest to the LAN (so that it's 
> transparent for IP traffic)

Done.

> -allow using a LAN-wide DHCP server for the Guest

Done by the above.

> -the host should be able to set up his LAN interface over the LAN-wide DHCP 
> server.

Done.

> -the host networking still works as before (at least on the layers above 
> Ethernet)

Done.

> -the whole thing is easy to set up

Done.

> -the whole thing can be started by any user at any time (so it's not started 
> at boot time, but whenever a user starts Qemu).

Requires root rights.

The restrictions to the above is that the guest can not reach the host in 
such setup.

Regards
Henrik