[libvirt] RFC: Supporting IPv6 on libvirt virtual networks

Pierre Ossman pierre-list at ossman.eu
Fri Nov 5 18:49:27 UTC 2010

On Tue, 02 Nov 2010 14:22:08 -0400
Laine Stump <laine at laine.org> wrote:

> There are a couple of bugzilla records open requesting IPv6 support on
> libvirt's virtual networks:
> https://bugzilla.redhat.com/show_bug.cgi?id=514749
> https://bugzilla.redhat.com/show_bug.cgi?id=586124
> This is a first cut at describing what that support will look
> like. Please send any comments/criticisms/suggestions you may have.

As a user I'm really looking forward to this. Without IPv6 support,
it's difficult to move away from the script based networking. (which in
turn doesn't play nice with a qemu locked down with SELinux)

>     prefix="<some number>"
>       Optional. This is used to specify how many significant bits are
>       in the ipv6 address. This will also be usable for ipv4, but the
>       parser will make sure that only one of netmask or prefix is given
>       for an ipv4 address (since netmasks generally aren't specified as
>       such in IPv6, the netmask attribute will not be allowed if family
>       is ipv6).

I suppose omitting this for IPv6 would be shorthand for the standard
64-bit prefix?

You write optional here, but your examples doesn't omit it so just so
I'm not misinterpreting I figure I'd ask. :)

>     So, I'm thinking we can add an <radvd/> subelement to IP that, for
>     now, will have no attributes and no subelements. If the ip/radvd
>     subelement exists, libvirt will send radvd a SIGHUP when the
>     network is brought up, and again if it is brought down.

I agree with the points already brought up in this thread. I would like
to request though that you keep this point that it is possible to not
have router advertisement. I don't have any actual failure scenarios to
motivate this, but I like the general principle of disabling features
that aren't necessary. :)

Given the scenario under which libvirt is commonly used, have you given
any thought to more dynamic prefix management? With IPv4 NAT "solves"
the issue of the machine moving around different connections. With
IPv6, something else is needed. I believe DHCPv6 can query for a
network that the machine in turn can delegate. Not sure how you
would go about getting that functionality connected to libvirt somehow
though. :)

Any idea of the time frame for getting basic support into the main
repo? And any plans for RHEL 6 given the "comprehensive IPv6
support"? :)

     -- Pierre Ossman

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