[libvirt] Proposal: no dnsmasq (no dhcp and no dns) and no radvd option

Laine Stump laine at laine.org
Tue Nov 20 22:29:43 UTC 2012

On 11/20/2012 02:36 PM, Gene Czarcinski wrote:
> Laine mentioned something yesterday that got me to thinking: being
> able to specify that dnsmasq is not to be started for an interface.
> Let me expand that by saying that libvirt would not start dnsmasq for
> either dns or dhcp and also would not start radvd.  However, the IPv4
> and IPv6 gateway addresses would be defined on the virtual network
> interface and the "usual" iptables and ip6tables rules would be in force.
> This would allow a user to configure dnsmasq to meet any user desires
> or use something completely different instead of dnsmasq.
> Questions:  Useful?  Worth the time and effort?

That was already determined before I mentioned it to you - it's been
requested several times, and I've told some people it was "going to
happen", although didn't say when :-).

>   And then there is how should this be specified in the network xml
> file? ... some new parameter?  ... A subperameter of <dns> such as
> <dns disable='yes' /> ?  ... a subparameter of <bridge> such as
> <bridge name="virbr0" dns="disable" /> ?

The <bridge> element is commonly *not* specified manually, but is filled
in automatically be libvirt, so I don't think it's a good place to put
optional flags (you would end up manually specifying settings for the
things that are automatically filled in, like the bridge name).

If anything, I would say the choice would be between putting it in <dns>
or in the toplevel <network>, i.e.:

      <dns disable='yes'/> (or maybe "<dns enable='no'/> is better)


    <network dns='no'>

Or, maybe it would be even better to put it in the <ip> element:

    <ip address='' netmask='' dns='no'/>

that way you could have dnsmasq listen on some of the IP addresses
defined for a network, but not others.

At the same time, we probably to be able to disable ipv6 RA as well.
Since that's only enabled when there is an ipv6 address, it can also be
added into the <ip> element config:

    <ip family='ipv6' address='f00d::1' ra='no'/> (or maybe
"autoconf='no'" ?)

Yeah, I think I like it best in <ip> (unless someone else has a better

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