[CentOS-mirror] IPv6 Mirroring

David Richardson david.richardson at utah.edu
Mon Aug 1 18:16:19 EDT 2011

On Mon, 1 Aug 2011, Kevin Stange wrote:

> On 08/01/2011 03:37 PM, Matt Domsch wrote:
>> On Mon, Aug 01, 2011 at 02:16:30PM -0500, Kevin Stange wrote:
>>> Karabir suggested we start getting together a list of steps that need
>>> completion to deliver an IPv6-preferenced or IPv6-only list of mirrors
>>> for IPv6-only clients using CentOS.
>> FWIW, Fedora hasn't had a significant need to IPv6-preferenced of
>> IPv6-only mirrors.  We do manage preference by ASN, netblocks (IPv4
>> and IPv6), internet2 (and related networks) and country.  Fedora does
>> have nameservers advertised on AAAA records, as well as A records.
>> The inbound web proxies are reachable via both AAAA and A records, so
>> MirrorManager does see a client's IPv6 or IPv4 address.
>> MirrorManager replies to client requests with DNS names. Mirrors may
>> themselves advertise a given name with an AAAA or A record.
> The idea would be to provide DNS names we know have AAAA records to
> provide better quality of service to a yum client that can't use A
> records.  Otherwise, it's a lot of poking randomly at hosts until one
> with AAAA is found.
> It's also just a good idea at this point to at least build the mirror
> infrastructure to be IPv6 capable from end to end so that an IPv6-only
> client at least has a shot at finding a mirror at all.

The question is: are we optimizing our service for ipv6-only clients, or 
for ipv6-capable (dual-stack) clients?

Returning only a list of v6-capable mirrors to a client will help the case 
of a v6-only client, but could hurt a v6-capable client.

One example problem: what do you do when there are no v6 mirrors in a 
country (since the mirror system today is country-based)? Do you return v4 
mirrors from that country, or v6 mirrors from other countries? Remember 
that in some countries international bandwidth can be very expensive.

I am a big proponent of ipv6 (my mirror has had a v6 address for years). 
However, running a client v6-only ignores the fact the most of the 
internet is still v4-only (let alone dual-stack). It's an interesting 
experiment, but a v6-only client is not very useful on today's internet 
(and probably won't be for several years). I don't think we should cater 
much to people who choose to make their own lives difficult.


David Richardson <david.richardson at utah.edu>
Center for High Performance Computing at the University of Utah
"It's possible to tell your mind what to do only when
  your mind agrees with you." -- Archie Goodwin, "A Family Affair"

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