Re: [Qemu-devel] Adding support for Stateless Static NAT for TAP devices

[Stefan Hajnoczi <stefanha@gmail.com>]

On Thu, Aug 30, 2012 at 09:12:19AM +0300, John Basila wrote:
> When running multiple instances of QEMU from the same image file
> (using -snapshot) and connecting each instance to a dedicated TAP
> device, the Guest OS will most likely not be able to communicate
> with the outside world as all packets leave the Guest OS from the
> same IP and thus the Host OS will have difficulty returning the
> packets to the correct TAP device/Guest OS. Stateless Static
> Network Address Translation or SSNAT allows the QEMU to map the
> network of the Guest OS to the network of the TAP device allowing
> a unique IP address for each Guest OS that ease such case.
> The only mandatory argument to the SSNAT is the Guest OS network
> IP, the rest will be figured out from the underlying TAP device.
> 
> Signed-off-by: John Basila <jbasila@checkpoint.com>
> ---
>  net/tap.c        |  369 +++++++++++++++++++++++++++++++++++++++++++++++++++++-
>  qapi-schema.json |    5 +-
>  qemu-options.hx  |   10 ++-
>  3 files changed, 381 insertions(+), 3 deletions(-)

This does not work with vhost=on because the host<->guest packet
processing happens in vhost_net.ko instead of in QEMU.

Use iptables on the host to NAT the tap interface.

Stefan