libvirt users - Apr 2014 - Re: Changing dnsmasq DNS settings for virtual machines

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Hi everyone,

maybe this is an old fart, but I cant get it to work.

I am running libvirt on a laptop, where a dnsmasq is already running
to delegate dns info for my local (not-public) network. My resolv.conf
(on the host) lists the system-dnsmasq as first server.

I had to set the listen-adress for the system-dnsmasq to 127.0.0.1 and
set bind-interfaces, to stop if from binding to all interfaces and
overriding the libvirtd-dnsmasq, which also has dhcp enabled.

Now, how can I tell the libvirtd-dnsmasq, to use the system-dnsmasq as
first nameserver?

I found lots of pages when searching for "libvirt dns", but all of
them only show the dhcp-part of the network's xml file:

http://wiki.libvirt.org/page/VirtualNetworking#DNS_.26_DHCP
> <ip address="192.168.122.1"
netmask="255.255.255.0"> <dhcp> <range
> start="192.168.122.100" end="192.168.122.254" />
<host
> mac="00:16:3e:e2:ed" name="foo.example.com"
ip="192.168.122.10" />
> </dhcp> </ip>
One possible workaround:
My system-dnsmasq reads /etc/hosts_whatever, and apparently the
libvirtd-dnsmasq reads var/lib/libvirt/dnsmasq/NETWORK_NAME.addnhosts.
I could copy my hosts_whatever in that place, but I had to configure
the libvirtd-dnsmasq what my local domains are.

Which brings me to the next question:
How to set the addn-hosts= for the libvirtd-dnsmasq in the xml file?

Regards,
Johannes
- -- 
A good sermon should be like a woman's skirt: short enough to arouse
interest but long enough to cover the essentials.
(Ronald Knox)
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On 06.04.14 07:33 Johannes Kastl wrote:
> Which brings me to the next question: How to set the addn-hosts> for the
libvirtd-dnsmasq in the xml file?
*ping*

Maybe I asked the wrong question, and this is an RTFM. But I looked
some more and found: nil. Nada. Nothing.

If someone had a M that I could F R then I would be glad... ;-)

Regards,
Johannes
- -- 
`Dobby is a free house-elf and he can obey anyone he likes´
(Harry Potter and the Half-blood Prince, S. 394)
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On 04/06/2014 08:33 AM, Johannes Kastl wrote:
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>
> Hi everyone,
>
> maybe this is an old fart, but I cant get it to work.
>
> I am running libvirt on a laptop, where a dnsmasq is already running
> to delegate dns info for my local (not-public) network. My resolv.conf
> (on the host) lists the system-dnsmasq as first server.
>
> I had to set the listen-adress for the system-dnsmasq to 127.0.0.1 and
> set bind-interfaces, to stop if from binding to all interfaces and
> overriding the libvirtd-dnsmasq, which also has dhcp enabled.
>
> Now, how can I tell the libvirtd-dnsmasq, to use the system-dnsmasq as
> first nameserver?
libvirtd's dnsmasq instances always forward requests that they can't
resolve themselves to the dns server listed in /etc/resolv.conf, so it
should already be doing what you want.

There was a bug in libvirt for quite awhile that caused
locally-unresolved requests for hostnames in the domain given by the
network's <domain name='xyzzy'/> element to be dropped rather
than
forwarded. Is that possibly the cause of your problems?

Alternately, since 1.1.3 you can tell dnsmasq to forward to a specific
address rather than the one listed in /etc/resolv.conf with the
<forwarder> subelement of the <dns> element in the network
definition, e.g.:

     <dns>
       <forwarder addr='1.2.3.4'/>
     </dns>

This is documented here:

   http://www.libvirt.org/formatnetwork.html#elementsAddress

There was a bug in libvirt for quite awhile that caused
locally-unresolved requests for hostnames in the domain given by the
network's <domain name='xyzzy'/> element to be dropped rather
than
forwarded. Is that possibly the cause of your problems?
>
> I found lots of pages when searching for "libvirt dns", but all
of
> them only show the dhcp-part of the network's xml file:
>
> http://wiki.libvirt.org/page/VirtualNetworking#DNS_.26_DHCP
>> <ip address="192.168.122.1"
netmask="255.255.255.0"> <dhcp> <range
>> start="192.168.122.100" end="192.168.122.254" />
<host
>> mac="00:16:3e:e2:ed" name="foo.example.com"
ip="192.168.122.10" />
>> </dhcp> </ip>
> One possible workaround:
> My system-dnsmasq reads /etc/hosts_whatever, and apparently the
> libvirtd-dnsmasq reads var/lib/libvirt/dnsmasq/NETWORK_NAME.addnhosts.
> I could copy my hosts_whatever in that place, but I had to configure
> the libvirtd-dnsmasq what my local domains are.
>
> Which brings me to the next question:
> How to set the addn-hosts= for the libvirtd-dnsmasq in the xml file?
You do that with the <host> subelement of the <dns> element. An
example
is at the same link as above.
>
> Regards,
> Johannes
> - -- 
> A good sermon should be like a woman's skirt: short enough to arouse
> interest but long enough to cover the essentials.
> (Ronald Knox)
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>

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On 10.04.2014 13:08 Laine Stump wrote:
> On 04/06/2014 08:33 AM, Johannes Kastl wrote:
>> There was a bug in libvirt for quite awhile that caused 
>> locally-unresolved requests for hostnames in the domain given by
>> the network's <domain name='xyzzy'/> element to be
dropped rather
>> than forwarded. Is that possibly the cause of your problems?
Maybe...
>> Alternately, since 1.1.3 you can tell dnsmasq to forward to a
>> specific address rather than the one listed in /etc/resolv.conf
>> with the <forwarder> subelement of the <dns> element in the
>> network definition, e.g.:
> 
>> <dns> <forwarder addr='1.2.3.4'/> </dns>
Nice, seems to work.
>> This is documented here:
> 
>> http://www.libvirt.org/formatnetwork.html#elementsAddress
I actually was on that page, but I must have missed that bit...
> Which brings me to the next question: How to set the addn-hosts> for the
libvirtd-dnsmasq in the xml file?
> 
>> You do that with the <host> subelement of the <dns>
element. An
>> example is at the same link as above.
No, thats not it. I do not want to set single hosts, I want to tell
dnsmasq to read an additional hosts-file. In the normal dnsmasq.conf
this is done via addn-hosts=, and that appears in the conf-file for
the network called e.g. WHATEVER:

addn-hosts=/var/lib/libvirt/dnsmasq/WHATEVER.addnhosts

Regards,
Johannes
- -- 
'Are you Death?'
... IT'S THE SCYTHE, ISN'T IT? PEOPLE ALWAYS NOTICE THE SCYTHE.
(Terry Pratchett, The Fifth Elephant)
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