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 practice.
- 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.
Thanks, Matt