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



On 11/21/2012 07:31 AM, Daniel P. Berrange wrote:
On Wed, Nov 21, 2012 at 07:18:20AM -0500, Gene Czarcinski wrote:
On 11/20/2012 05:29 PM, Laine Stump wrote:
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.:

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

or

     <network dns='no'>
       ...
     </network>

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

     <ip address='192.168.122.1' netmask='255.255.255.0' 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
idea).
Not really better since I like the idea of adding this to <ip>.
However, I believe this is wrong!  it is a mistake to tie this to an
IP address.  Look at the problems that have occurred with dnsmasq.
I agree, we should let this be controlled independently of
the <ip> tag. You might want to allow DNS, without defining
any IP elements at all.
Mmmm. The only way this could work is if --interface=<virbrnn> was specified. Right now, if no IPv4 or IPv6 addresses are specified, this this is not a virtual gateway device but a virtual network interface for very isolated guest-to-guest only communications. [see patch I just submitted to make IPv6 have the same functionality as IPv4].

Instead, I suggest that this be an expansion to <network>.
  For example, <network dns='no'>.  This could also scratch
an itch of mine for specifying logging:
  <network dnslog='yes" dhcplog='yes'>.  Then there is the
issue with bind-intererface and bind-dynamic:
  <network bind='dynamic'>
Since you envisage multiple config parameters related to
DNS, this argues for a top level <dns> element to group
them all together.

   <network>
     ...
     <dns.../>
     ...
   </network>
Yes, dns currently has two possible items: dns=yes/no and dnslog=noyes. But dhcplog=no/yes and bind=interface/dynamic are not really related to dns. I suggest just keeping it simple and at a single level under <network>. I hope I am making my point understandable because I am not sure of the terminology used for discussing xml.

Gene


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