When checking for DNS issues, you might find that your nameserver is not responding to queries even though the relevant zone file exists in the server and the named service is running.
In some cases, the named service will not respond because it is misconfigured.
Running the following command might show useful information about your configuration:
Note: You might also find that the named service will not be able to restart while in a misconfigured state. And if the named service is down and no longer listening on port 53, this could result in port 53 appearing to be closed from the outside.
Backup your current named configuration:
Run the following script to rebuild the named.conf file and restart the named service: