Using domain PTR vs Only IP?

Server operators
1

Hello;

NTP poll allows us to add only with ip for public servers. Why some servers have PTR records + a record? What is the difference between them_?

Thank you!

2

PTR records are actually unrelated to this. They’re for reverse DNS.

If you have set up your DNS so that your NTP server ntp.example.com resolves to an IP address, you can add ntp.example.com to the pool and the pool management page will then show “192.0.2.42 / ntp.example.com” ie. both IP and name. Some people have added their servers to the pool by IP address only, which is also OK. The DNS name is for informative purposes only and is only used/shown on the management page.

3

Not really.

PTR is not needed for the pool. But it looks nice as the chronyc/ntpd pages do a reverse hostname lookup and then show the PTR. When the PTR isn’t set, it shows the name of what your ISP assigned.

The A record is needed when you want to start your own pool, like I have for my own systems.

root@server:~# nslookup ntp.heppen.be
Server:		127.0.0.1
Address:	127.0.0.1#53

Non-authoritative answer:
Name:	ntp.heppen.be
Address: 212.187.8.48
Name:	ntp.heppen.be
Address: 185.142.225.68
Name:	ntp.heppen.be
Address: 51.75.149.45
Name:	ntp.heppen.be
Address: 87.118.104.17
Name:	ntp.heppen.be
Address: 2001:1b60:2:1:1126:104:0:1
Name:	ntp.heppen.be
Address: 2001:41d0:700:1e9d::ec3d:bd92

root@server:~# nslookup 185.142.225.68 
68.225.142.185.in-addr.arpa	name = ntp.heppen.be.

However, you do need a static-IP to join the pool, else your server will be set non-functional if your IP changes a lot.

The pool does not use DNS-records, other then when you add them. So can I add my servers all at once by just entering my pool. Pretty handy. But my servers do a tiny bit more then ntp-only, so the PTR and A/AAAA records where already there :grin: