Re: [Qemu-devel] [PATCHv7 9/9] qapi-schema, qemu-options & slirp: Adding Qemu options for IPv6 addresses

[Daniel P. Berrange]

On Wed, Feb 10, 2016 at 01:45:22PM +0100, Samuel Thibault wrote:
> Thomas Huth, on Wed 10 Feb 2016 12:39:10 +0100, wrote:
> > > +    if (!vprefix6) {
> > > +        vprefix6 = "fec0::";
> > 
> > Site-local prefixes have already been deprecated (see rfc3879) ... would
> > it be feasible to use a ULA prefix instead (fd00::/8,
> > see rfc4193) ?
> 
> The question is which ULA. Ideally we'd take a random one at each qemu
> startup, but then it's a pain for users to type IPs by hand, all the
> more so when it changes at each qemu startup. Another way is to have the
> same in all qemu instances, hardcoded in qemu, i.e. like
> 
> https://xkcd.com/221/
> 
> proposes. That's still a pain to type, even if it is always the same,
> and can still (since it's the same for all qemu instances) pose some of
> the problems raised by rfc3879. The rfc1918 addresses we use in qemu
> for ipv4 have the same issues. That's why I considered that the issues
> mentioned by rfc3879 would not be relevant to qemu, and be simpler to
> just use fec0::, and let the user chose his public or ULA prefix if he
> needs it.

I'm inclined to agree that fec0:: is a better bet for QEMU's default
usage, despite rfc3879. As you say it is no worse than what we have
with IPv4, and IMHO it is preferrable to using a fixed ULA since that
would be non-compliant with the RFC which requires randomness.

Regards,
Daniel
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