Re: [libvirt] [PATCH] network: don't use dhcp-authoritative on static networks
On Sun, 2016-12-18 at 20:37 -0500, Laine Stump wrote:
On 12/16/2016 11:58 AM, Martin Wilck wrote:
> "Static" DHCP networks are those where no dynamic DHCP range is
> defined, only a list of host entries is used to serve permanent
> IP addresses. On such networks, we don't want dnsmasq to reply
> to other requests than those statically defined. But
> "dhcp-authoritative" will cause dnsmasq to do just that.
> Therefore we can't use "dhcp-authoritative" for static networks.
Not surprising that this simple change would have unexpected
consequences - that seems to be a basic law of the universe :-)
ACK to this, but it has me wondering 1) what is the range for which
it
returns a positive response? Is it for anything within the IP
address/netmask of the interface it's listening on? Or something
larger
than that? (Does it just blindly ACK any request it gets?) and 2) Do
we
know for certain that the same thing doesn't happen when there is
also a
dhcp range defined?
I can't answer this for certain at the moment. I got a report from our
cloud people and this patch fixed their configuration; I haven't seen
it in my own environment.
Wrt 2), I'd bet that the same thing will happen with a DHCP range
defined. But would that be wrong? If dnsmasq is allowed to take IP
addresses from a dynamic range, why shouldn't it do so (*)? Several
DHCP servers in the same subnet are a strange configuration anyway. In
the case of the "static" network it makes a certain amount of sense (in
our case, the libvirt DHCP server was only used to serve the IP of a
single static host, which was then used as DHCP server for all other
hosts on the network), but if a "dynamic" dhcp service already exists,
adding another one looks like begging for trouble to me.
I can try to figure stuff out in more detail, but it'll take some time.
Regards,
Martin
(*) I can see a corner case: when libvirt dnsmasq's dynamic range was
depleted. Should it be allowed to respond to queries in that case?
Sorry, I don't know.
--
Dr. Martin Wilck <mwilck(a)suse.com>, Tel. +49 (0)911 74053 2107
SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton
HRB 21284 (AG Nürnberg)