libvirt users - Feb 2018 - Re: libvirt and NAT on a system that already has a DHCP server

I'm trying to use virt-manager and qemu/kvm on Arch Linux. The box I'm
using is also the router for my house. It runs a kea DHCP server. When I
try to start the default NAT network, it can't start dnsmasq because that
port is already bound. Is there a way to have it not bind on this
interface? I see there is an except-on statement in the dnsmasq.conf, but
I can't add lines to that directly, and I didn't see any way to add
special options using virsh net-edit default.

Thanks.

On 01/30/2018 07:37 PM, john@bluemarble.net wrote:
> I'm trying to use virt-manager and qemu/kvm on Arch Linux. The box
I'm
> using is also the router for my house. It runs a kea DHCP server. When I
> try to start the default NAT network, it can't start dnsmasq because
that
> port is already bound. Is there a way to have it not bind on this
> interface? I see there is an except-on statement in the dnsmasq.conf, but
> I can't add lines to that directly, and I didn't see any way to add
> special options using virsh net-edit default.
The dnsmasq processes run by libvirt to serve dhcp for the virtual
networks already does this - they listen *only* on the bridge created
for their particular network, nothing else. Your problem is that your
host system's dhcp server has been configured to automatically listen on
all interfaces.

So it's not the configuration of the libvirt network that needs to
change, it's the configuration of the host system's dhcp server. It
needs to be told that it shouldn't automatically listen on all new
interfaces, but to just listen on certain specific interfaces.

On Thu, Feb 01, 2018 at 09:19:11AM -0500, Laine Stump
wrote:
> On 01/30/2018 07:37 PM, john@bluemarble.net wrote:
> > I'm trying to use virt-manager and qemu/kvm on Arch Linux. The box
I'm
> > using is also the router for my house. It runs a kea DHCP server. When
I
> > try to start the default NAT network, it can't start dnsmasq
because that
> > port is already bound. Is there a way to have it not bind on this
> > interface? I see there is an except-on statement in the dnsmasq.conf,
but
> > I can't add lines to that directly, and I didn't see any way
to add
> > special options using virsh net-edit default.
> 
> The dnsmasq processes run by libvirt to serve dhcp for the virtual
> networks already does this - they listen *only* on the bridge created
> for their particular network, nothing else. Your problem is that your
> host system's dhcp server has been configured to automatically listen
on
> all interfaces.
> 
> So it's not the configuration of the libvirt network that needs to
> change, it's the configuration of the host system's dhcp server. It
> needs to be told that it shouldn't automatically listen on all new
> interfaces, but to just listen on certain specific interfaces.
Checkout this

https://wiki.libvirt.org/page/Libvirtd_and_dnsmasq

Regards,
Daniel
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