How to Resolve Websites Not Accessible in Plesk Due to Stopped DNS Server

Pre-requirements

• Administrator access to Plesk control panel.
• Basic knowledge of DNS configurations and services in Plesk.
• Root or sudo access to the Linux server for troubleshooting network issues.

Issue

Websites hosted on Plesk become inaccessible, and DNS zones fail to synchronize via the Slave DNS Manager extension. Attempting to connect to port 53 using telnet locally results in a connection failure:

telnet localhost 53

Cause

The issue occurs when the DNS Server (BIND) service is stopped in Plesk. This prevents DNS queries from being processed, rendering websites inaccessible.

Resolution

To resolve the issue, restart the DNS Server (BIND) service from the Plesk control panel:

Steps to Restart DNS Server (BIND) in Plesk

1. Log into Plesk as an administrator.
2. Navigate to Tools & Settings > Services Management.
3. Find the DNS Server (BIND) service in the list.
4. Click the button next to DNS Server (BIND) to restart the service.
5. Verify that the service is running by checking the status in Services Management.
6. Test website accessibility again and confirm that DNS synchronization via the Slave DNS Manager is functioning.

Gotchas to Avoid

• • Ensure the BIND service is set to start automatically after a reboot. You can check this by running:

systemctl enable named

• If the service fails to start, check the system logs for any additional errors in /var/log/messages or /var/log/syslog.
• Ensure that firewall settings allow traffic on port 53 (TCP/UDP) for DNS queries.

Linux Commands to Check DNS Server Status

• • Check if BIND is running:

systemctl status named

• • Start the DNS Server if not running:

systemctl start named

• • Enable the DNS Server on boot:

systemctl enable named

Pre-requirements

• Root or sudo access to the server.
• Basic understanding of network port testing and troubleshooting tools.

Risk of Using Telnet for Port Testing

Telnet is an older tool commonly used to test network port connectivity. However, it is considered insecure as it does not encrypt any data sent over the connection. Using Telnet for network testing can expose sensitive information, making it vulnerable to interception.

Alternatives to Telnet and How to Use Them

1. Using netcat (nc)

netcat, also known as nc, is a more secure and flexible tool for testing network ports. It supports both TCP and UDP connections and can be used to verify DNS port 53 connectivity:

1. 1. Install netcat if it's not already available on your system:

# For Ubuntu/Debian:
sudo apt-get install netcat

# For CentOS/RHEL:
sudo yum install nc

1. 1. Test port 53 on the server:

nc -zv localhost 53

• -z: Scan without sending data.
• -v: Enable verbose output to display results.

Connection to localhost 53 port [tcp/domain] succeeded!

1. If the port is closed or filtered, you’ll receive an error message indicating the issue.

2. Using nmap

nmap (Network Mapper) is another powerful tool for scanning and troubleshooting network ports. It can be used to check if port 53 is open on your DNS server:

1. 1. Install nmap if it's not installed:

# For Ubuntu/Debian:
sudo apt-get install nmap

# For CentOS/RHEL:
sudo yum install nmap

1. 1. Run nmap to scan port 53 on localhost:

nmap -p 53 localhost

1. Analyze the output:

• If port 53 is open, you will see it listed as "open" in the results.
• If it's closed or filtered, adjust your firewall settings or start the DNS service as needed.

3. Using ss (Socket Statistics)

ss is a modern replacement for the netstat tool and can be used to check if a service is listening on a particular port. To verify if BIND is listening on port 53, run:

ss -tuln | grep ':53'

• -t: Show TCP sockets.
• -u: Show UDP sockets.
• -l: Show only listening sockets.
• -n: Show numerical addresses instead of resolving names.

Gotchas to Avoid

• Ensure you're using a secure method like netcat or nmap instead of telnet for testing ports.
• Always check firewall settings if you encounter issues with port connectivity.
• Test both TCP and UDP ports when troubleshooting DNS issues, as DNS typically uses UDP but can also operate over TCP in certain cases.

Linux Commands to Verify DNS Port Status

• • Check BIND service status:

systemctl status named

• • Check for DNS port listening:

ss -tuln | grep ':53'

For more detailed troubleshooting and alternative methods, visit our Knowledge Base.