[libvirt] dnsmasq option "dhcp-authoritative" in libvirt virtual networks?

[Jim Fehlig]

On 09/19/2016 09:48 AM, Martin Wilck wrote:
> Hello,
>
> I am seeing a slightly annoying behavior of libvirt-created networks on
> my system. Whenever a VM fails to renew its DHCP lease in time (for
> example because my laptop is suspended), the IP address changes,
> causing various annoyances. If this happens, the log message
> "DHCPNAK(virbrX): ... lease not found" appears in the libvirtd logs. 
>
> Looking at the dnsmasq code, it seems that this would be fixed by
> running dnsmasq with the "dhcp-authoritative" option, which, according
> to the dnsmasq man page, "should be set when dnsmasq is definitely the
> only DHCP server on a network" - IMO that's the case for libvirtd-
> managed virtual networks. So the question comes to my mind: is there a
> good reason why libvirtd doesn't set "dhcp-authoritative" on the
> dnsmasq instances it starts?

I've searched the list archives and didn't see any mention of the
'--dhcp-authoritative' option, so the reason may be that no one has made such an
inquiry :-). If it has been discussed and I missed it, Laine most likely knows
something about it.

A small bit of detective work shows that OpenStack neutron adopted use of this
option a while back

https://review.openstack.org/#/c/152080/

In a related discussion, Simon agrees with using '--dhcp-authoritative' when
dnsmasq is the only dhcp server on the network

http://lists.thekelleys.org.uk/pipermail/dnsmasq-discuss/2015q1/009171.html

I also stumbled across a complaint about using '--dhcp-authoritative' on a
network with multiple dhcp servers, but I can't find that now. I'm not sure if
there are use-cases for multiple dhcp servers on a single libvirt virtual network.

Regards,
Jim