Common DNS Errors and How to Troubleshoot Them

Categories: DNS Management

The Domain Name System (DNS) is critical for connecting users to websites. However, DNS errors can disrupt this process, leading to issues like inaccessible websites or failed email delivery. Understanding common DNS errors and knowing how to troubleshoot them can help minimize downtime and maintain a seamless online experience.

1. DNS_PROBE_FINISHED_NXDOMAIN

What It Means:

This error indicates that the domain name cannot be resolved because it does not exist in the DNS records.

Common Causes:

• Incorrect DNS records (e.g., A, CNAME, or MX records)

• Expired domain registration

• Misconfigured DNS settings on the client or server

Troubleshooting Steps:

1. Verify the domain registration status using WHOIS tools.

2. Check DNS records via your DNS provider’s dashboard.

3. Clear the DNS cache on your local machine using commands like:

   • On Windows: ipconfig /flushdns

   • On macOS/Linux: sudo dscacheutil -flushcache or sudo systemd-resolve --flush-caches

4. Test the domain with tools like dig or nslookup to verify DNS resolution.

2. DNS Server Not Responding

What It Means:

Your device is unable to communicate with the DNS server.

Common Causes:

• Network connectivity issues

• Overloaded or offline DNS servers

• Incorrect DNS server configuration

Troubleshooting Steps:

1. Check your internet connection.

2. Switch to a public DNS service like Google DNS (8.8.8.8) or Cloudflare (1.1.1.1).

3. Restart your modem/router to refresh network settings.

4. Verify DNS settings in your network adapter configuration.

3. SERVFAIL

What It Means:

The DNS server encountered a failure and could not complete the query.

Common Causes:

• DNSSEC validation issues

• Misconfigured DNS zones

• Server resource limitations

Troubleshooting Steps:

1. Disable DNSSEC temporarily to check if it’s causing the issue.

2. Verify zone file configurations and correct any errors.

3. Restart the DNS server or increase its resources if under heavy load.

4. REFUSED

What It Means:

The DNS server refused to answer the query.

Common Causes:

• Misconfigured access control lists (ACLs) on the server

• Server is set to respond only to specific IP ranges

• Firewall blocking DNS traffic

Troubleshooting Steps:

1. Check and update ACLs to allow queries from the affected clients.

2. Ensure the server is configured to accept queries from public IPs if required.

3. Verify firewall settings to ensure port 53 (used for DNS) is open.

5. Timeout Errors

What It Means:

The DNS query took too long to complete, resulting in a timeout.

Common Causes:

• Slow or overloaded DNS servers

• Network latency or packet loss

• Recursive queries taking too long to resolve

Troubleshooting Steps:

1. Test DNS resolution using alternative servers to rule out server-specific issues.

2. Optimize DNS settings by reducing recursion depth.

3. Use tools like traceroute to identify network bottlenecks.

4. Monitor DNS server performance and scale resources as needed.

6. Mismatch in DNS Records

What It Means:

Inconsistent or incorrect DNS records cause resolution issues.

Common Causes:

• Typographical errors in DNS records

• Conflicting records for the same domain (e.g., duplicate A records)

• Missing or outdated records

Troubleshooting Steps:

1. Audit DNS records for errors or conflicts.

2. Update records to match current hosting and email server configurations.

3. Use DNS validation tools to ensure proper record formats.

7. CNAME Loops

What It Means:

A CNAME record points to another CNAME record in a loop, causing infinite redirection.

Common Causes:

• Improperly configured CNAME chains

Troubleshooting Steps:

1. Review CNAME records and ensure they ultimately resolve to an A or AAAA record.

2. Simplify CNAME chains to reduce complexity.

Tools for Diagnosing DNS Errors

• dig and nslookup: Command-line tools for querying DNS servers.

• DNS Checker: Online tool to check DNS propagation globally.

• Pingdom and UptimeRobot: Monitor DNS and website availability.

• Google Public DNS Troubleshooting Tool: Diagnose issues with Google DNS.

Final Thoughts

DNS errors can disrupt your online presence, but understanding their causes and knowing how to troubleshoot them can minimize downtime and improve reliability. Regularly monitor your DNS records, use reliable DNS providers, and implement best practices like caching and redundancy to prevent issues before they arise. With the right tools and approach, you can keep your domain running smoothly.