[CentOS-mirror] IPv6 Mirroring

Matt Domsch Matt_Domsch at dell.com
Mon Aug 1 16:37:59 EDT 2011

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.

>  Here's what I've got so far.  Feel
> free to add to it:
> Steps are in order of priority:
> - Establish at least two authoritative name servers for centos.org with
> v6 IPs.
> - Determine if centos.org registrar supports v6 glue, transfer to a
> registrar that supports it if needed, then add the glue.
> - Augment the current mirror database with a field for IPv6 support and
> IPv4 support, filling in IPv4 as enabled for all existing mirrors.
> - Build a list of centos mirrors which have AAAA records and/or consult
> with mirror admins to identify the mirrors which are prepared to provide
> preferred IPv6 connectivity to IPv6 clients.
> - Prepare a separate monitoring system for IPv6 content to confirm that
> mirrors are serving the content correctly over both v4 and v6.

Right now Fedora's MM crawler runs on machines that can only speak
IPv4.  I trust mirror admins that if they're advertising both AAAA and
A records, that both methods are equivalent and if one works, the
other works.  I haven't had a significant problem with this in

> - Modify the mirror list on mirrorlist.centos.org to provide IPv6
> mirrors with a higher priority than IPv4 mirrors when the client
> accesses it via its AAAA address rather than A.
> - Add AAAA for mirrorlist.centos.org
> Thoughts?

Are there a bunch of mirrors for whom IPv6 bandwidth is "free",
compared to IPv4?  That's the only reason I can see going to this
effort.  I understand that bandwidth via Internet2 would be cheaper
than commercial links, which is why MM sends I2-capable clients to
I2-capable servers first.  Otherwise, seems like a lot of work for not
necessarily any gain.


Matt Domsch
Technology Strategist
Dell | Office of the CTO

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