IPv6 issue on TestBot?

Maarten Lankhorst m.b.lankhorst at gmail.com
Thu Sep 22 11:30:57 CDT 2011


On 09/22/2011 04:54 PM, Michael Stefaniuc wrote:
> Per Johansson wrote:
>> 22 sep 2011 kl. 12:14 skrev Michael Stefaniuc:
>>> Wow! /66? And that works? While the standard allows for that you "should
>>> use /64" which everybody and his dog read it as that is the only thing
>>> that needs to work and the only thing that get tested. IPv6 brings back
>>> the class-full thinking which everybody has to painfully unlearn once
>>> IPv6 catches on...
>>> "Safe" prefix length (especially if involving client devices) are:
>>> /64 - LAN
>>> /126 and /127 - point to point
>>> /128 - host routes
>> RFC3513 is quite more strict than "should":
> Which is obsoleted by RFC4291, but that seems to have kept this
> paragraph. Anyway the correct RFC term to make it mandatory is "must".
> And it isn't a "must". Also the RFC4291 is from 2006 which is *old*.
>>    All global unicast addresses other than those that start with binary
>>    000 have a 64-bit interface ID field (i.e., n + m = 64), formatted as
>>    described in section 2.5.1.  Global unicast addresses that start with
>>    binary 000 have no such constraint on the size or structure of the
>>    interface ID field.
>> (2001:: has the binary prefix 001). So this might very well be the problem.
> The same RFC4291 says:
>    Except for the knowledge of the subnet boundary discussed in the
>    previous paragraphs, nodes should not make any assumptions about the
>    structure of an IPv6 address.
> It might be the problem but not because of the RFC; it just might be a
> typo as it is a manually set IP.
>> I've heard the reason for 64 bits is that it's what currently fits in most computer registers, but I don't know if it's true.
> What really helps to understand IPv6 is:
> - IPv6 is an old protocol >15 years. That predates the Internet taking over.
> - IPv6 was designed based on the assumption that it will make the
> Internet again a friendly, warm and cozy place; a big any to any network
> without barriers/firewalls.
> - IPv6 isn't better than IPv4, it is different.
> - IPv4 still outperforms IPv6 in the new feature development. IPv6 is
> trying to play catch up. A few things that were long ago deprecated in
> IPv4 are still mandatory for IPv6 to be "standards compliant".
> - Don't assume that if the IPv6 standard says something the
> implementations really follow that. Test, test, test.
> So no, the /64 host part has nothing to do with current hosts having
> 64bit registers now. I'm pretty sure that they were hoping to have
> 128bit computers by now. It had more to do with thinking that a globally
> unique identifier for the host is a good think to have and the MAC
> address already provided that with 48bits. But 48 isn't a nice number so
> it was rounded up to 64 which makes for a nice "design" as it is half of
> the IPv6 address.
Discussion aside, seems that using /64 works, so I'm keeping that.
With the change testbot.winehq.org works again when using ipv6.
I am not sure why it was set to /66, so I just hope nothing breaks as
a result of this change.


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