I see no reason, no reason whatsoever, to only give 2.pool.ntp.org an AAAA record. Let’s enable AAAA on the others too.
Just looking at the server count, there appears to be merit in enabling the use of IPv6 on another of the entries. Or maybe not. I will have to do some digging. Right now if everyone was on IPv6 I assume the clients would all prioritize IPv6 for each of the numeric entries, meaning that right now they’d talk to IPv6 servers 25% of the time. Adding one more AAAA record would bring that up to a 50/50 split.
IPv4 IPv6 Africa 37 16 Asia 177 90 Europe 1680 982 North America 632 302 South America 45 12 Oceania 92 36 Global 2660 1426
IOW, 35% (1426 / (1426 + 2660)) of the pool servers are on IPv6. Since the minimum number of servers configured is 3, the current setup, which provides AAAA records only for the
2.pool.ntp.org name, roughly matches the current distribution of IPv6 servers in the pool.
However, when using just the name
pool.ntp.org, perhaps with the
pool directive, no AAAA records are returned. Given the current fraction of IPv6 servers in the pool, it should return at least one AAAA record among the four, which would still provide three servers to IPv4 only clients.
Perhaps returning AAAA records for the name
3.pool.ntp.org could be considered too.