IPv6 support

Eventually the plan is, of course, to support IPv6 in the pool system. It's not a high priority item yet though.

If you do have your system setup with IPv6, please follow the timekeepers list for announcements and related discussions.

Implementation plan

Not breaking IPv4 hosts is, for now, more important than supporting IPv6.

The plan is to make a "beta.pool.ntp.org" zone first and have that tested, likely for a long period of time. One of the potential issues is hosts with ipv6 configured but no routes. Various NTP implementations and network setups will have to be tested. Currently for example ntpd doesn't retry on IPv4 if IPv6 fails ("bug 334":https://support.ntp.org/bugs/show_bug.cgi?id=334). Yes, it's pretty silly that IPv6 is made so that's necessary, but that's what we have.

If necessary we'll eventually deploy IPv6 support in "ipv6.pool.ntp.org" but preferably we can do it with AAAA records in the regular zones.

Martin v. Löwis: It might be sensible to deploy ipv6.pool.ntp.org instead of beta.pool.ntp.org. Initially, there would be only a small number of v6-capable servers, so having per-area subsets might not work for a long time. Also, it's not clear (to me), whether GeoIP support would be available for clients accessing the DNS through IPv6.

To register IPv6 servers in the pool, the UI needs to be changed to accept IPv6 addresses. pool1.v2.diff implements such a change, also providing a fallback for failing Geo::IP lookups. The first version ( pool1.diff ) of the patch took a different approach, allowing a single server to be assigned both v4 and v6 addresses.

Dependencies

Before doing IPv6 support some of the things we need to do first are

 * Upgrade the DNS system
 * Distributed monitoring system

In Subversion the full todo which might have a few more details on some of these items.

Martin v. Löwis: Doing full monitoring might not be necessary as long as each server has both IPv4 and IPv6 addresses; the existing monitoring software will tell whether the server itself becomes offline or starts ticking incorrectly. A regular check that the IPv6 addresses respond at all to NTP requests might be sufficient.

DNS

From the point of view of the new DNS system, this needs to be done.

• Add support for AAAA requests in pgeodns (this is now implemented: ipv6.v2.diff )
• Set up a couple DNS servers on IPv6.
• Alter the mysql database on www.pool.ntp.org to store IPv6 addresses
• Generate a ntp_servers_ipv6.cdb file for IPv6.