[CentOS-mirror] IPv6 Mirroring

Wed Aug 3 11:34:11 UTC 2011
Marko Bevc <marko at bevc.net>


I would agree. IPv6 has nothing to do with mirror manager. It is a 
protocol wich client uses or not. If you have AAAA records and are on dual 
stack you will prefer to go thru IPv6. Otherwise if there is also A/CNAME 
record you will go over IPv4.

On Tue, 2 Aug 2011, Matt Domsch wrote:

> On Tue, Aug 02, 2011 at 11:42:47AM -0500, Kevin Stange wrote:
>> On 08/02/2011 10:10 AM, Matt Domsch wrote:
>>> On Mon, Aug 01, 2011 at 05:45:16PM -0500, Kevin Stange wrote:
>>>> We'd be catering to v6-capable (dual stack) clients by offering
>>>> mirror choices with v6 ahead of v4 if the client seems to prefer v6.
>>> Here's where I start to lose you.  We don't presently have a way for a
>>> client to indicate to anyone anywhere that it "prefers" v6 instead of
>>> v4, or vice versa.  From the server side, it sees a connection, either
>>> on v6 or on v4, and sees an address.  We would have to add a flag into
>>> the yum mirrorlist request URL to give the client an opportunity to
>>> note its preference.  Not hard technically, but the obvious
>>> implementation would require manual configuration by each end user,
>>> and that's nearly never done.
>>> How would you envision a client recognizing that it should prefer v6
>>> over v4, automatically?  Solving that cleanly, the rest is
>>> straightforward.
>> We can tell if a client prefers v6 because it will access
>> mirrorlist.centos.org using its IPv6 address.  The client doesn't need
>> to tell us explicitly because its decision to access the v6 address
>> means it's decided to try the AAAA first.
> With all due respect, I disagree.  Apps on a dual-stack system will
> use IPv6 if they can, then IPv4, at a system level, provided an IPv6
> address is provisioned to the system.  It has nothing to do with
> connectivity between the system and any other mirror server on the
> internet, which is what mirrors are trying to solve.
>> I suppose we could compile a list of prefers_v6 mirrors, but my thoughts
>> didn't extend past concluding that if the client prefers v6 by evidence
>> we just offer it the v6 mirrors sorted first so it can use the preferred
>> protocol.
> I understand, but I don't think that's a good indicator for
> preference, and I think specifying one protocol is preferred over
> another doesn't buy us much.
>> Do you think it's likely that mirrors will prefer avoiding v6 if they
>> have enabled it?
> No.  If they advertise both, they'll accept both.  There's no way to
> specify a mirror's preference for one or the other, just as there is
> no way to specify a client's preference.  If they want to avoid v6,
> they simply don't advertise an AAAA record. :-)
> MirrorManager (and the respected MirrorBrain) aim to solve for the
> "best" mirror on the assumption that closer mirrors network-wise are
> preferred over mirrors that are further away, irrespective of a
> client's IPv4 or IPv6 address.  Both offer ways to direct clients to
> preferred servers based on network characteristics (BGP ASNs, network
> blocks) between client and potential servers, and only then falling
> back to GeoIP, all of which are protocol agnostic (both v4 and v6 are
> supported).
> Thanks,
> Matt

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