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Re: [libvirt] libvirt plans: dns support for IPv6?



On 09/13/2012 04:05 PM, Laine Stump wrote:
On 09/13/2012 02:00 PM, Gene Czarcinski wrote:
I would like to know what the plans are for supporting dns for virtual
guests with only IPv6.

My objective is to be able to reference a virtual guest for the host
... doing ssh, scp, etc.  such functions work just fine if you specify
the ip-address but, after a while, those ip-addresses are difficult to
remember ... afterall, that is why dns exists.

For IPv4, with a some patches to libvert implementing "--local=/virt/
--domain-needed" if "--domain virt" is specified, I am now able to ssh
to guests by name.

The additions needed are to run the NetworkManager supporting
"--conf-dir=/etc/NetworkManager/dnsmasq.d/" (or patch it like I did),
and add a file specifying the dnsmasq on the virtual NIC.  For
example, server=/virt/,192.168.122.1 will forward queries.

Alternatively, you can run yet another dnsmasq on the host which just
passes queries to the dnsmasq and modify your upstream dns server to
forward any queries for the virtual domains to the dnsmasq on the host.

IPv6 is another situation entirely.  And it may be even more important
to have dns support because if IPv4 address are difficult to remember,
IPv6 are practically impossible.

So, are there any plans for providing dns on the IPv6 virtual networks?

I can see a couple of solutions and each has pluses and minuses.

1. Do it the same way the it is done for IPv4.  The current version of
dnsmasq (2.63) supports dhcp for IPv6 and, IIRC, has since 2.61. I
realize that you need to continue support of libvirt on RHEL 6 and
possibly others that are running an old version of dnsmasq, but isn't
it time to move along?  While you can manually configure IPv6
interfaces so that you can add the definitions to a /etc/host file,
this is not a good approach from my perspective.  The use of dnsmasq
also allows specification of different domains for each virtual IPv6
network.

2. There is another approach and it would be useful for both dnsmasq
and this approach be available.  That is, continue to use radvd and
have the virtual guests autoconf the ip addresses.  Then use mDNS
(avahi and nss-mdns) to support access by name.  This does not require
doing anything about dnsmasq.  In fact, it is possible thatyou do not
need it at all.  In addition, the plans for Fedora 18 are to make mDNS
the default for Desktop installs [I am not sure what that means].  A
big problem is that there is only a single domain which is ".local" by
default.  An even bigger problem is that ssh (openssh) has an error if
a mDNS name is specified.

I noticed that Daniel Berrange has put in a bugzilla request that
dnsmasq be updated.

If someone is already coding up patches to add dhcp for IPv6 or will
"real soon now", I will be happy to test it.  Otherwise, I could take
a shot at coming up with the patches.
AFAIK nobody else is working on that right now, so I'd say go for it :-)


OK ... I guess :-) I started looking at the code and I believe that I am going to learn a lot more about libvirt that I thought I would have to. Well, this is something I believe needs doing.

Gene


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