virtual network with qemu

Nikos Vassiliadis nvass9573 at
Thu May 14 13:08:26 UTC 2009

marco.borsatino at wrote:
> First, thank you. You are right, qemu has an internal DHCP server,
> which should be perfect for me, becuse I would like to emulate a
> network without any contact with external (real) world. The problem
> is that my virtual PC can't ping the gateway. For my idea (this is
> just a way to study a project for a network without a real network)
> the communication is intended only among virtual PCs. But If I can't
> contact the (virtual) gateway will it be possible to contact another
> virtual PC on a different subnet? Or even on the same subnet? In my
> idea I would like to create a little but complex net with one master
> controller, a slave controller, a little number of client belonging
> to different subnets. Maybe with or without a DHCP server.

Yes, hosts on the same IP network, which of course are on the same
broadcast domain, are able to communicate with each other with no
other intermediates. A gateway is required only if you want to
communicate with other networks. So, you have to create, let's say,
3 virtual PCs:
1) host_a on network A
2) host_b on network B
3) router_a on both networks A and B

That's all.

I guess, qemu uses the multicast solution to create virtual
broadcast domains, like a switch does. qemu, I guess, has no
knowledge of what happens on these ethernets, like a real ethernet
switch. It's a real cool solution, since the user is able to
create networks than can span several physical machines.

Maybe you should use socket instead of mcast, don't really
know the pros and cons of those two.

Last but not least, since you seem to look for a learning tool, let
me suggest two great ones:
1) imunes, you need vmware player for a quick start.
2) netkit

I have extensively used imunes and it's great.
You should also check netkit. In case, it matters, the latter
is GNU/Linux based.

HTH, Nikos

More information about the freebsd-questions mailing list