DNS zone update in Plesk times out

Symptoms

• During any DNS record change or addition in Plesk the page times out, however, the change is applied.
• The following error message is output to /var/log/plesk/panel.log with the debug mode enabled:

  Error code 1: rndc: connect failed: 203.0.113.2#953: timed out

Cause

Connection to one of the slave DNS servers is not possible:

# nmap 203.0.113.2 -p953
...
Host is up (0.0087s latency).
PORT STATE SERVICE
953/tcp filtered rndc
Nmap done: 1 IP address (1 host up) scanned in 0.65 seconds

Resolution

Make sure that connection is possible from the slave server side by opening TCP port 953.