CentOS 7 : NTPd (wierd?) behaviour with FQDN vs IP

Nitin

4/20/23, 11:30 AM

I recently setup NTP server on my environment, along with DNS. And when I configure an NTP client, I see the below behaviour:

[root@template ~]# host mydns.mydomain.ops
mydns.mydomain.ops has address 10.10.5.2
[root@template ~]# grep mydns.mydomain.ops /etc/ntp.conf
server 0.mydns.mydomain.ops iburst
[root@template ~]# systemctl status ntpd
● ntpd.service - Network Time Service
   Loaded: loaded (/usr/lib/systemd/system/ntpd.service; enabled; vendor preset: disabled)
   Active: active (running) since Mon 2021-12-20 16:38:54 IST; 10min ago
  Process: 724 ExecStart=/usr/sbin/ntpd -u ntp:ntp $OPTIONS (code=exited, status=0/SUCCESS)
 Main PID: 737 (ntpd)
   CGroup: /system.slice/ntpd.service
           └─737 /usr/sbin/ntpd -u ntp:ntp -g
[root@template ~]# ntpq -pn
10.10.5.2: timed out, nothing received
***Request timed out
[root@template ~]#

However, if I happen to replace the FQDN in my /etc/ntp.conf with the IP address (and ofcourse restart the service), it works just perfectly fine:

[root@template ~]# grep 10.10.5.2 /etc/ntp.conf
server 10.10.5.2 iburst
[root@template ~]# ntpq -pn
     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
*10.10.5.2      192.46.15.60     3 u   44   64  377    0.251   11.240   4.310

I'm kind of confused how DNS resolution is failing only for NTP. Is there something else I'm overlooking? Please help ...

0 + 0

domain-name-system

ntpd

centos7

AlexD

4/20/23, 12:10 PM

In the first example, you use `mydns.mydomain.ops` with `host` command but your `ntp.conf` has `0.mydns.mydomain.ops`. In the same first example `ntpq -pn` prints `10.10.5.2` and this indicates that DNS resolution is working.

Elon Musk

I sit in a Tesla and translated this thread with Ai:

EN: CentOS 7 : NTPd (wierd?) behaviour with FQDN vs IP

TH: CentOS 7: พฤติกรรม NTPd (แปลก ๆ ?) กับ FQDN เทียบกับ IP

RO: CentOS 7: Comportament NTPd (ciudat?) cu FQDN vs IP

RU: CentOS 7: поведение NTPd (странное?) с полным доменным именем и IP

VI: CentOS 7: Hành vi NTPd (kỳ lạ hơn?) với FQDN so với IP

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