Make ntp work out of the box at IPv6-only sites

[brooks]

Summary

NTP pools {0,1,3}.freebsd.pool.ntp.org contain only NTP servers
wtth IPv4 addresses only. Whereas the NTP pool 2.freebsd.pool.ntp.org
contains servers with IPv4 and IPv6 addresses. Use it instead.
This allows FreeBSD installed at IPv6-only sites to work out
of the box.

While here, document all four pools, allowing the user to uncomment
one of the other NTP pools when desired.

See PR/264088.

Test Plan

Tested here and by person who reported PR/264088.

[cy]

Interestingly, {0,1,3}.{freebsd,fedora,debian,ubuntu}.pool.ntp.org support only IPv4. While 2.{freebsd,fedora,debian,ubuntu}.pool.ntp.org all support IPv4 and IPv6.

[emaste]

Interestingly, {0,1,3}.{freebsd,fedora,debian,ubuntu}.pool.ntp.org support only IPv4. While 2.{freebsd,fedora,debian,ubuntu}.pool.ntp.org all support IPv4 and IPv6.

They return (some of) the same addresses, as with 0.pool.ntp.org. Having this work out of the box with IPv6 is important but we should probably discuss this with ntp.org folks?

[cy]

In D35268#799384, @emaste wrote:

Interestingly, {0,1,3}.{freebsd,fedora,debian,ubuntu}.pool.ntp.org support only IPv4. While 2.{freebsd,fedora,debian,ubuntu}.pool.ntp.org all support IPv4 and IPv6.

They return (some of) the same addresses, as with 0.pool.ntp.org. Having this work out of the box with IPv6 is important but we should probably discuss this with ntp.org folks?

Probably. I have access to their internal buzilla. I'll raise it there.

In the meantime let's put this on ice.

[bz]

I've lately seen a lot of DNS64 responses for ntp on startup on dev machines where I don't have a specific config... would be nice to make that go away...

[brooks]

Superseded by D39954. Commandeering to close