DNS Server Unavailable: How to Fix DNS Server Issues

We are in the modern internet era, and despite everything being so advanced, there are still issues that many people are still grappling with. One of the most prevalent being DNS server issues. Encountering a “DNS server unavailable” error, or any other DNS-related issue, can bring everything to a halt, quite literally. These issues, responsible for nearly 80% of network outages, disrupts the fundamental process that translates human-readable domain names into IP addresses—the cornerstone of online communication. DNS servers process billions of queries daily, and even minor disruptions can cascade into significant connectivity problems. So, how can you fix these issues if you encounter it? This answers that question comprehensively and by the end, you will be able to restore optimal network functionality.

What is a DNS server?

A DNS server, or Domain Name System server, is a critical component of internet infrastructure that translates human-readable domain names (like www.example.com) into IP addresses (such as 192.0.2.1) that computers use to identify each other on the network. Essentially, it acts as an internet directory or phone book, allowing users to access websites and other online resources by typing in easy-to-remember domain names instead of numerical IP addresses. DNS servers enable efficient routing of internet traffic and ensure users can connect to the desired websites and services seamlessly.

As for ‘DNS server unavailable’ issue, it is a common network problem that can disrupt internet connectivity and access to online resources. When this error occurs, it means that a user’s device is unable to communicate with the DNS server to resolve domain names into IP addresses, which is essential for locating and connecting to websites and other online services. Here are some technical details about the issue:

DNS Query Process: When you enter a URL into your browser, your device sends a DNS query to a DNS server. The DNS server then translates the human-readable domain name into an IP address that computers use to communicate with each other. If the DNS server is unavailable, this translation cannot occur, and the browser cannot access the site.

DNS Hierarchy: The DNS system is hierarchical, with root servers at the top, followed by top-level domain (TLD) servers, and then authoritative name servers. Issues can occur at any level of this hierarchy, potentially causing broader unavailability if problems arise higher up in the structure.

Client-Side and Server-Side: The problem can originate on the client side (e.g., incorrect DNS settings on your computer or router) or the server side (e.g., the DNS server you’re trying to reach is down). Diagnosing the source of the problem is crucial for effective troubleshooting.

Identifying the ‘DNS server unavailable’ issue

Inability to Access Websites – The most immediate and noticeable symptom is the inability to load websites. When a DNS server is unavailable, typing a URL in a browser results in an error message, such as “DNS server not found” or “Server DNS address could not be found.”

Intermittent Connectivity – Users may experience intermittent connectivity where the internet works sporadically. This inconsistency can be particularly frustrating as it may appear that the network connection is unreliable.

Delayed Connections – There might be significant delays in accessing websites or online services. The device may take a long time to resolve domain names, resulting in slow browsing experiences.

Email and Other Services – Apart from web browsing, other services that rely on DNS resolution, like email clients, online gaming, and video conferencing, can also be affected, leading to broader disruptions in productivity and communication.

What are the common causes of a DNS server becoming unavailable?

A DNS server can become ‘unavailable’ due to a variety of reasons. Here are some common causes:

• Network Connectivity Issues – Problems with the network, such as a disconnected cable, malfunctioning router, or issues with the ISP, can prevent access to the DNS server.
• Server Configuration Errors – Misconfigurations in the DNS server settings can lead to it being unreachable or unresponsive.
• DNS Server Outages – The DNS server itself may be down due to maintenance, hardware failures, or power outages.
• Firewall or Security Software Interference – Firewalls, antivirus software, or other security measures may block DNS queries, making the server appear unavailable.
• DNS Cache Corruption – Corrupted or outdated DNS cache on the client side can prevent proper resolution of domain names.
• Software Bugs – Bugs in the DNS server software or the client software can cause the DNS server to become unavailable.
• Router or Modem Issues – Faulty or misconfigured routers and modems can block DNS traffic, rendering the server unreachable.
• ISP Issues – Problems at the ISP level, such as misrouting or server mismanagement, can lead to DNS server unavailability.
• DNS Attacks – Cyberattacks such as DNS spoofing, DDoS attacks, or DNS cache poisoning can disrupt DNS server operations, making them inaccessible.
• High Traffic Volume – A sudden surge in DNS requests can overwhelm the server, causing it to fail or become unresponsive.
• Outdated Firmware or Software – Running outdated firmware on network devices or outdated software on the server can lead to compatibility issues and unavailability.

Immediate Fixes for DNS Server Unavailability

If you encounter a “DNS server unavailable” issue, there are several immediate fixes you can try to restore your internet connectivity. These solutions address common problems that can disrupt DNS resolution.

Reset Your DNS Settings to Fix the Issue

1. Windows

• Open the Control Panel.
• Navigate to Network and Sharing Centre.
• Click on Change adapter settings.
• Right-click on your network connection and select Properties.
• Select Internet Protocol Version 4 (TCP/IPv4) and click Properties.
• Choose “Obtain an IP address automatically” and “Obtain DNS server address automatically.”
• Click OK and restart your compute

2. macOS

• Open System Preferences.
• Click on Network.
• Select your network connection (Wi-Fi or Ethernet).
• Click on Advanced.
• Go to the DNS tab.
• Remove any custom DNS servers by selecting them and clicking the minus (-) button.
• Click OK and Apply.

3. Linux

• Open the terminal.
• Edit your network configuration file. For Ubuntu, this is typically /etc/network/interfaces or /etc/netplan/*.yaml.
• Set DNS to be obtained automatically (e.g., dhcp).
• Restart your network service with sudo systemctl restart NetworkManager or sudo /etc/init.d/networking restart.

Flush the DNS Cache on Different Operating Systems

“Flush the DNS Cache” refers to the process of clearing out the Domain Name System (DNS) cache on a computer or network device. The DNS cache is a temporary database maintained by an operating system or network device that stores information about recent DNS lookups. Flushing the DNS cache can resolve issues caused by corrupted or outdated DNS information.

How to Flush the DNS Cache

The method to flush the DNS cache depends on the operating system being used. Here are instructions for some common systems:

Windows

1. Open the Command Prompt as an administrator. You can do this by searching for “cmd” in the Start menu, right-clicking on Command Prompt, and selecting “Run as administrator.”
2. Type the following command and press Enter: ipconfig /flushdns
3. You should see a message confirming that the DNS Resolver Cache has been successfully flushed.

macOS

1. Open the Terminal. You can find it in Applications > Utilities > Terminal.
2. Type the following command and press Enter. The specific command varies slightly depending on the macOS version:

• For macOS Catalina and later: sudo dscacheutil -flushcache; sudo killall -HUP mDNSResponder
• For earlier versions of macOS: sudo killall -HUP mDNSResponder

Linux

1. Open the Terminal.
2. The command can vary depending on the Linux distribution and DNS service being used.

• For systems using ‘systemd-resolved,’ use: sudo systemd-resolve –flush-caches
• For systems using dnsmasq, use: sudo /etc/init.d/dnsmasq restart
• For systems using nscd, use: sudo /etc/init.d/nscd restart

Restart Your Modem and Router to Resolve DNS Issues

Sometimes, network issues can be resolved by simply restarting your modem and router. This can refresh the connection and clear any temporary issues affecting DNS resolution.

• Power off your modem and router – Unplug the power cables from both the modem and the router.
• Wait for about 30 seconds – This allows the devices to completely shut down and clear any residual memory.
• Plug in the modem first – Wait for the modem to fully restart and establish a connection to your ISP (usually indicated by stable lights).
• Plug in the router – Wait for the router to fully restart and establish a connection with the modem.
• Reconnect your devices – Once both devices are fully operational, reconnect your computer or other devices to the network.

Other measures to fix DNS-related issues

Other than the immediate fixes we have listed above, there are other things you can try to fix the problem.

Change Your DNS Server Settings to an Alternative Server

Changing your DNS server settings to an alternative server can help fix DNS-related issues, improve internet speed, enhance security, and provide better reliability. By default, your internet service provider (ISP) assigns you a DNS server, but these may not always be the most efficient or secure.

Here are some well-regarded alternative DNS servers you can consider:

Google Public DNS

• Primary DNS: 8.8.8.8
• Secondary DNS: 8.8.4.4
• Benefits: Known for its speed, reliability, and widespread global infrastructure. It is designed to improve browsing performance and security.

OpenDNS

• Primary DNS: 208.67.222.222
• Secondary DNS: 208.67.220.220
• Benefits: Offers robust security features, including phishing protection and content filtering. OpenDNS provides customisable settings and is popular for its reliability and enhanced security options.

Cloudflare DNS

• Primary DNS: 1.1.1.1
• Secondary DNS: 1.0.0.1
• Benefits: Focuses on speed and privacy. Cloudflare promises not to log user data and offers one of the fastest DNS services available. It also provides additional security features to protect against cyber threats.

How to Change DNS Settings on Windows

1. Open Network and Sharing Centre:

• Right-click on the network icon in the system tray and select Open Network & Internet settings.
• Click on Network and Sharing Centre.

2. Change Adapter Settings:

• Click on Change adapter settings on the left-hand side.

3. Open Properties:

• Right-click on your active network connection (e.g., Ethernet or Wi-Fi) and select Properties.

4. Select Internet Protocol Version 4 (TCP/IPv4):

• Highlight Internet Protocol Version 4 (TCP/IPv4) and click Properties.

5. Enter New DNS Server Addresses:

• Select Use the following DNS server addresses.
• Enter the preferred DNS server (e.g., 8.8.8.8 for Google Public DNS) and the alternate DNS server (e.g., 8.8.4.4 for Google Public DNS).
• Click OK to save the changes.

6. Repeat for Internet Protocol Version 6 (TCP/IPv6) (optional):

• Highlight Internet Protocol Version 6 (TCP/IPv6) and click Properties.
• Enter preferred and alternate DNS server addresses for IPv6 (e.g., 2001:4860:4860::8888 and 2001:4860:4860::8844 for Google Public DNS).
• Click OK to save the changes.

How to Change DNS Settings on macOS

• Open System Preferences, click on the Apple menu and select System Preferences.
• Then go to Network Settings and click on Network.
• Select Your Network Connection – Choose your active network connection (Wi-Fi or Ethernet) from the list.
• Open Advanced Settings and click on Advanced.
• Change DNS Servers:
• Go to the DNS tab.
• Click the plus (+) button to add new DNS server addresses.
• Enter the new DNS server addresses (e.g., 8.8.8.8 and 8.8.4.4 for Google Public DNS).
• Remove any existing DNS servers by selecting them and clicking the minus (-) button.
• Click OK to save the changes, then Apply to confirm.

How to Change DNS Settings on Linux

• Open Network Manager: Access Network Manager through your system settings or the network icon in your taskbar.
• Select Network Connection: Choose your active network connection (e.g., Wired or Wireless).
• Edit Connection: Click on the settings or edit icon (typically a gear or wrench).
• Go to IPv4 or IPv6 Settings: Navigate to the IPv4 or IPv6 tab.
• Change DNS Servers:
• In the DNS field, enter the new DNS server addresses (e.g., 8.8.8.8, 8.8.4.4 for Google Public DNS).
• Ensure that the method is set to Automatic (DHCP) addresses only if you are entering manual DNS servers.
• Save the changes and restart your network connection.

How to Change DNS Settings on a Router

• Access Router’s Web Interface:
• Open a web browser and enter your router’s IP address (commonly 192.168.1.1 or 192.168.0.1) into the address bar.
• Log in with your router’s username and password.
• Locate DNS Settings: Navigate to the DNS settings section, which is often found under settings like Internet, WAN, or DHCP.
• Enter New DNS Server Addresses:
• Enter the new DNS server addresses in the provided fields (e.g., 8.8.8.8 and 8.8.4.4 for Google Public DNS).
• Some routers may offer fields for both primary and secondary DNS servers.
• Save and Apply Changes: Save the changes and reboot your router if necessary.

Advanced Troubleshooting solutions

When basic fixes don’t resolve DNS server issues, advanced troubleshooting techniques can help identify and solve deeper problems. Here’s how you can use various tools and methods for advanced DNS troubleshooting.

Using the Command Prompt or Terminal for Advanced DNS Troubleshooting

The Command Prompt (Windows) or Terminal (macOS/Linux) offers several commands to diagnose and resolve DNS issues. They include;

Using ping to Test DNS Server Availability

• Open Command Prompt or Terminal:
• On Windows, press Windows + R, type cmd, and press Enter.
• On macOS/Linux, open the Terminal from your applications or use a shortcut (e.g., Ctrl + Alt + T on some Linux distributions).
• Ping the DNS Server:
• Type ping 8.8.8.8 (or the IP address of your DNS server) and press Enter.
• If the DNS server is reachable, you will see replies indicating successful communication. If you get a timeout or error message, the server may be unavailable or unreachable due to network issues.

Using nslookup to Diagnose DNS Issues

• Open Command Prompt or Terminal: Follow the steps mentioned above to open your command-line interface.
• Run nslookup:
• Type nslookup and press Enter.
• Enter a domain name (e.g., nslookupgoogle.com) and press Enter.
• nslookup will display the IP address associated with the domain name and the DNS server used for the query. If the command fails, it can indicate a DNS resolution problem.
• Check DNS Server:
• You can specify a DNS server by typing nslookup www.google.com 8.8.8.8.
• This tests if a specific DNS server can resolve the domain name, helping identify if the issue is with your default DNS server.

Use tracert (Windows) or traceroute (macOS/Linux) to Identify Where the Connection Fails

• Open Command Prompt or Terminal: Follow the steps mentioned above to open your command-line interface.
• Run tracert or traceroute:
• On Windows, type tracert www.google.com and press Enter.
• On macOS/Linux, type traceroute www.google.com and press Enter.
• These commands trace the path packets take to reach the specified domain, showing each hop along the way. If the trace fails at a specific point, it can help identify where the connection issue lies.

Configure and use DNS logging for deeper diagnostics

Configuring and using DNS logging for deeper diagnostics can help you troubleshoot DNS-related issues, monitor traffic, and enhance security by identifying unusual patterns or malicious activities. Here’s a step-by-step guide on how to enable and use DNS logging:

Enable DNS Logging on Windows:

• Open Event Viewer by typing eventvwr.msc in the Run dialog (Windows + R).
• Navigate to Applications and Services Logs > Microsoft > Windows > DNS-Server.
• Enable DNS server logs to capture detailed information about DNS queries and responses.

Enable DNS Logging on Linux:

• Edit the DNS server configuration file (e.g., /etc/bind/named.conf for BIND).
• Add logging options to capture detailed query logs.
• Restart the DNS server with sudo systemctl restart bind9 or the relevant command for your DNS server.

Analyse Logs:

Review the log files to identify patterns, errors, or unusual activity that may indicate the source of DNS issues.

How VPNs Affect DNS Server Functionality and How to Troubleshoot This

VPN DNS Settings

• VPNs often use their own DNS servers, which can override your system settings. This can cause DNS resolution issues if the VPN’s DNS servers are slow or unresponsive.
• Check the VPN settings to see if it uses custom DNS servers and change them if necessary.

Split Tunneling

• Enable split tunneling if available. This allows you to route DNS queries outside the VPN tunnel, using your default DNS servers instead of the VPN’s servers.

Test Without VPN

• Disconnect from the VPN and test your DNS functionality. If the issue is resolved, the problem may lie with the VPN’s DNS settings or servers.
• Contact your VPN provider for support if the issue persists while connected to the VPN.

Network-Level Solutions

When DNS server issues persist despite troubleshooting on individual devices, addressing potential problems at the router level can often resolve the situation. Here’s how to approach DNS troubleshooting, firmware updates, and necessary network setting adjustments on your router.

Troubleshoot DNS Server Issues at the Router Level

• Restart the Router: Power cycle the router by unplugging it from the power source, waiting about 30 seconds, and plugging it back in. This can resolve temporary issues affecting DNS resolution.
• Check DNS Settings:
• Access the router’s web interface by entering its IP address (commonly 192.168.1.1 or 192.168.0.1) into a web browser.
• Log in with your router’s credentials (username and password).
• Navigate to the DNS settings section, often found under Internet, WAN, or DHCP settings.
• Ensure the DNS server addresses are correct. Consider changing to reliable DNS servers like Google Public DNS (8.8.8.8 and 8.8.4.4) or Cloudflare (1.1.1.1 and 1.0.0.1).
• Test DNS Resolution
• Use the built-in diagnostics tools on your router (if available) to test DNS resolution.
• Some routers have a ping or traceroute feature that can help identify connectivity issues to the DNS server.
• Check for Network Conflicts: Ensure there are no IP address conflicts within your network. Assign static IP addresses carefully and avoid using the same IP address for multiple devices.
• Review Router Logs: Check the router’s logs for any errors or warnings related to DNS. These logs can provide insights into what might be causing the DNS issues.

Update Your Router’s Firmware to Resolve DNS Server Unavailability

• Find the Router Model and Firmware Version:
• Access the router’s web interface as described above.
• Locate the current firmware version and model number, usually found in the System Information or Status section.
• Download the Latest Firmware:
• Visit the manufacturer’s website and navigate to the support or downloads section.
• Find your router model and download the latest firmware version available.
• Backup Current Settings: Before updating, back up your current router settings. This option is typically available in the Administration or Maintenance section of the router’s interface.
• Update the Firmware:
• Go to the firmware update section in your router’s web interface (often under Administration or Maintenance).
• Follow the instructions to upload and install the new firmware. This process may take several minutes, and the router may reboot during the update.
• Restore Settings (if necessary): If you encounter issues after the update, you can restore the previously backed-up settings from the backup file.

Network Settings That Might Need Adjustment to Fix DNS Server Problems

• DNS Server Configuration: Ensure that the router’s DNS settings are correctly configured. You may need to manually enter DNS server addresses if they are not obtained automatically from your ISP.
• DHCP Settings
• Verify that the DHCP server on the router is correctly distributing IP addresses and DNS settings to all devices on the network.
• Make sure the DHCP lease time is appropriate for your network usage to prevent frequent renewals that could disrupt connectivity.
• MTU (Maximum Transmission Unit) Size: An incorrect MTU size can cause fragmentation and connectivity issues. Ensure the MTU size is set to the default value (usually 1500) unless your ISP recommends otherwise.
• QoS (Quality of Service): If your router supports QoS, ensure it is configured to prioritise DNS traffic appropriately. Misconfigured QoS settings can delay DNS queries and responses.
• Firewall Settings
• Check the router’s firewall settings to ensure that DNS traffic (port 53) is not being blocked.
• Some advanced security settings may inadvertently block or restrict DNS queries.
• Parental Controls and Filters
• Review any parental controls or content filtering settings that might interfere with DNS resolution.
• Ensure that any restrictions do not block access to necessary DNS servers or domains.
• Static IP and DNS Assignments:
• For devices that require a stable connection, consider setting static IP addresses and DNS server addresses directly on the devices.
• This can help avoid issues with DHCP server inconsistencies on the router.

ISP and External Factors

Understanding when to involve your ISP and recognising external factors affecting DNS servers can be crucial in maintaining a stable internet connection. Here’s how to approach these issues.

External Factors that could be Affecting DNS Servers

Planned Maintenance – ISPs and DNS service providers periodically perform maintenance to update and improve their infrastructure. During these times, DNS servers may be temporarily unavailable. ISPs typically notify customers of planned maintenance in advance.

Unplanned Outages – Power outages, hardware failures, or network disruptions at the ISP or DNS service provider’s end can cause DNS servers to become unavailable. These outages can be localised or widespread, affecting many users simultaneously.

Network Congestion – High traffic volumes or network congestion can lead to slow DNS responses or timeouts. This often occurs during peak usage times or due to large-scale events causing a surge in internet activity.

Natural Disasters – Severe weather events or natural disasters can damage infrastructure, leading to extended outages and affecting DNS servers and other critical services.

When Should You Contact Your ISP About DNS Server Unavailability?

Persistent DNS Issues Across Multiple Devices – If multiple devices on your network experience DNS server unavailability despite troubleshooting on individual devices and the router, it’s likely an issue beyond your local network.

After Eliminating Local Causes – Contact your ISP if you’ve exhausted common troubleshooting steps (e.g., resetting your router, changing DNS settings) without resolving the issue. This includes ensuring your router’s firmware is up to date and checking for any network misconfigurations.

ISP-Provided DNS Servers – If you’re using your ISP’s DNS servers and they consistently fail to respond or are slow, your ISP needs to investigate potential problems on their end.

Unexplained Internet Outages – When you experience frequent internet outages that correlate with DNS server unavailability, your ISP might be facing broader network issues that require their intervention.

Technical Support Confirmation – If you’ve confirmed that the issue isn’t with your network hardware or settings, reaching out to your ISP’s technical support can provide insights into whether they are experiencing widespread DNS problems or outages.

DNS Security and Best Practices

Securing your DNS settings is critical to maintaining the integrity and privacy of your internet traffic. Implementing best practices and advanced security protocols can protect your DNS queries from various threats.

• Use Reliable DNS Providers – Choose reputable DNS providers known for their security and reliability, such as Google Public DNS, Cloudflare, or OpenDNS.
• Regularly Update Router and Firmware – Keep your router and DNS server firmware up to date to protect against vulnerabilities and exploits.
• Implement DNSSEC – Enable DNS Security Extensions (DNSSEC) to ensure that the responses to DNS queries are authentic and have not been tampered with.
• Configure Firewalls – Set up firewalls to filter DNS traffic and block unauthorised access. Ensure that port 53 (used for DNS queries) is protected.
• Enable DNS Logging and Monitoring – Regularly monitor DNS logs to detect unusual activity that may indicate an attack. Set up alerts for suspicious patterns or excessive traffic.
• Use Encrypted DNS Protocols – Adopt DNS over HTTPS (DoH) or DNS over TLS (DoT) to encrypt DNS queries, protecting them from interception and tampering.
• Employ Rate Limiting – Implement rate limiting on DNS queries to prevent abuse and mitigate the impact of DDoS attacks.
• Restrict Recursive Queries – Configure DNS servers to restrict recursive queries to trusted clients only, reducing the risk of DNS amplification attacks.
• Use DNS Filtering – Deploy DNS filtering to block access to known malicious domains, enhancing security by preventing access to harmful sites.

Final thought

Ensuring your DNS server remains available and secure is essential for maintaining a reliable and safe internet experience. Addressing common issues, staying updated with the latest security practices, and leveraging advanced troubleshooting tools can significantly enhance DNS performance. By adopting encrypted DNS protocols, regularly updating firmware, and employing robust security measures, you can protect your network from various threats and ensure seamless connectivity. With these strategies in place, you can confidently navigate and manage DNS server challenges, ensuring a smooth and secure online environment for all users on your network.