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

[Thomas Huth]

On 10.02.2016 14:08, Daniel P. Berrange wrote:
> 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.

Ok, then let's go with fec0:: first. We still can change it later if
necessary.

 Thomas