SSL (Secure Sockets Layer) certificates play a crucial role in securing communication between a client (e.g., a web browser) and a server. They ensure the integrity and privacy of data exchanged by encrypting the communication. However, when issues arise in DNS (Domain Name System) settings, SSL certificates may not function as intended, causing various errors. This can have significant implications for website performance, user trust, and security.The purpose of this knowledge base article is to explain how DNS issues can cause SSL certificate errors and how to resolve them efficiently. We will cover key concepts related to SSL certificates and DNS, outline the common errors caused by DNS misconfigurations, and provide a step-by-step guide to troubleshooting and resolving SSL certificate errors.

Understanding SSL Certificates and DNS

What is an SSL Certificate?

An SSL certificate is a cryptographic protocol designed to protect the privacy and integrity of data exchanged between clients and servers. When a website is secured with SSL, it enables HTTPS (Hypertext Transfer Protocol Secure) connections, indicating that data is being transmitted securely.

How DNS Relates to SSL

DNS is responsible for resolving domain names to IP addresses. In the context of SSL certificates:

• DNS ensures that users are directed to the correct server, which is critical for SSL certificates to work properly.
• The SSL certificate issued by a Certificate Authority (CA) is tied to a specific domain or subdomain. If DNS settings are not correctly configured, it can cause SSL errors, as users may be sent to the wrong server or domain, resulting in certificate mismatches.

Common SSL Errors Caused by DNS Misconfigurations

SSL Certificate Mismatch Error

Description: This error occurs when the domain name on the SSL certificate does not match the domain name the user is attempting to access. For example, if your SSL certificate is issued for www.example.com, but users are accessing example.com without the "www" subdomain, they might encounter an SSL certificate mismatch.

DNS Cause: A misconfigured DNS record, such as missing or incorrect CNAME or A records, can cause the request to be routed to the wrong server or IP address, causing the SSL certificate mismatch.

SSL Certificate Not Trusted (Untrusted Certificate Error)

Description: This occurs when the browser does not trust the SSL certificate, usually because the certificate is self-signed or the certificate chain is incomplete.

DNS Cause: DNS issues that result in misrouting users to an outdated or incorrect server can lead to this error. For example, if the user is redirected to a server that has an outdated SSL certificate or the server fails to serve the correct intermediate certificates.

SSL/TLS Handshake Failure

Description: An SSL/TLS handshake failure occurs when the client and server cannot establish a secure connection. This could be due to various reasons, including incorrect SSL configurations on the server or network issues.

DNS Cause: Incorrect DNS settings can lead to users connecting to a server that doesn't have the correct SSL configuration, leading to handshake failures.

Mixed Content Errors

Description: This error occurs when a website is loaded over HTTPS, but some elements (e.g., images, scripts, stylesheets) are being loaded over HTTP, making the page insecure.

DNS Cause: If DNS records are not pointing to the correct server or if the server is misconfigured, resources may be loaded from an insecure server, causing mixed content errors.

Step-by-Step Guide to Resolve SSL Certificate Errors Caused by DNS

Verify DNS Records

Check A and CNAME Records

Ensure that the DNS records for your domain are pointing to the correct server IP address.

• A Records: Ensure that the A record for example.com (or www.example.com) is pointing to the correct IP address of the server hosting the SSL certificate.
• CNAME Records: If you're using a CNAME record (e.g., www.example.com pointing to example.com), verify that it is properly configured.

Verify DNS Propagation

After making changes to DNS records, it can take time for the changes to propagate across the global DNS network. Use tools like WhatsMyDNS to check the status of DNS propagation and ensure the domain resolves to the correct server worldwide.

Check for DNS Conflicts

Ensure there are no conflicting DNS records, such as multiple A records pointing to different servers for the same domain or conflicting CNAME records.

Verify SSL Certificate Configuration

Ensure SSL Certificate Matches the Domain

• Check the Common Name (CN): The CN in your SSL certificate should match the domain you're trying to access. For instance, www.example.com should be listed in the certificate as the CN.
• Check Subject Alternative Names (SAN): If the SSL certificate is a multi-domain certificate, make sure that the domain or subdomain you're accessing is included in the SAN list.

Ensure the Full Certificate Chain is Installed

Sometimes SSL errors occur because the intermediate certificates required to establish trust are missing. Ensure that the full certificate chain is installed, including the root certificate and any intermediate certificates. You can use SSL tools like SSL Labs' SSL Test to check if your certificate chain is correctly configured.

Check SSL Configuration on the Server

• Ensure the server is properly configured to serve the SSL certificate for the domain.
• Verify that the server supports the latest SSL/TLS protocols and ciphers.

Check for DNS Caching Issues

DNS caching issues can cause SSL errors, especially when the DNS record has been recently updated. If users are still directed to an old server after DNS changes, SSL certificate errors might occur.

Clear DNS Cache

Instruct users to clear their DNS cache, especially if they are experiencing SSL issues after DNS updates. This can be done by running the following commands:

• Windows: Open Command Prompt and type ipconfig /flushdns.
• macOS: Open Terminal and type sudo killall -HUP mDNSResponder.
• Linux: Use sudo systemd-resolve --flush-caches or restart the DNS resolver service.

Check ISP DNS Cache

In some cases, ISPs might cache old DNS records for longer periods than expected. Users experiencing SSL errors may be using outdated DNS information. Instruct users to either use a different DNS resolver (like Google's 8.8.8.8) or wait for DNS propagation to complete.

Resolve Mixed Content Issues

Mixed content errors can occur if your website loads some resources over HTTP while the page itself is loaded over HTTPS. These errors can trigger warnings or break the SSL encryption.

Force HTTPS

Ensure that all resources (images, scripts, etc.) are loaded over HTTPS by:

• Enforcing HTTP-to-HTTPS redirects in the web server configuration.
• Updating URLs within your site’s codebase to point to HTTPS versions of resources.

Update External Resources

If your website loads external resources (e.g., ads, third-party APIs) over HTTP, ensure that the external providers support HTTPS. If they don't, consider switching to a different provider or hosting the resources yourself.

Common DNS Issues Affecting SSL Certificates and How to Fix Them

Incorrect Nameservers

Issue: If the domain's nameservers are not configured correctly, users may be directed to the wrong server, which may not have the correct SSL certificate.

Solution: Double-check the nameserver settings at your domain registrar and ensure they point to the correct DNS provider or server hosting the SSL certificate.

DNS Misrouting

Issue: DNS misrouting can occur when DNS records are configured to point to the wrong IP address, potentially leading to a mismatch between the SSL certificate and the domain.

Solution: Verify the DNS A records, CNAME records, and any load balancer or proxy configurations to ensure they are pointing to the correct IP address.

Subdomain Configuration Issues

Issue: SSL certificates are often issued for a specific domain or subdomain (e.g., www.example.com). If the DNS record for a subdomain is not configured properly, SSL certificate errors may occur.

Solution: Ensure that DNS records for all subdomains match the SSL certificate. If you're using a wildcard certificate (*.example.com), ensure that the subdomains are properly routed to the correct server.

DNS TTL Settings

Issue: TTL (Time to Live) settings that are too long can cause outdated DNS records to persist even after changes are made, leading to SSL certificate errors.

Solution: Reduce TTL values before making DNS changes to allow for faster propagation. After DNS changes, monitor the TTL to ensure the new settings are recognized promptly.

Troubleshooting SSL Certificate Errors Due to DNS Misconfigurations

Use SSL Diagnostic Tools

• SSL Labs' SSL Test: A comprehensive tool that checks your SSL certificate's validity and configuration.
• DNSstuff: Use this tool to check DNS records and identify potential misconfigurations.

Check Server Logs

Review the web server and SSL error logs to pinpoint any specific SSL handshake or certificate-related issues caused by DNS misconfigurations.

Test on Different Devices and Networks

Test the website on multiple devices and networks to rule out local caching or ISP-level caching issues. You can also use a VPN to test DNS resolution from different geographical locations.

Usage Field, Technical Issue, and Technical FAQ for Resolving SSL Certificate Errors Caused by DNS

Usage Field for Resolving SSL Certificate Errors Caused by DNS

E-Commerce Websites

• Importance of SSL: SSL certificates on e-commerce sites ensure that user transactions are secure. Any DNS-related SSL issues can result in insecure connections, causing users to abandon purchases.
• Zero Downtime Migration: Ensuring SSL certificates function smoothly during DNS migration is crucial to avoid financial losses and protect customer data.

Corporate Websites

• Corporate Reputation: SSL certificates are critical for brand trust. SSL errors due to DNS misconfigurations can result in browsers flagging the site as insecure, which impacts the company’s credibility.
• Mitigation: Correct DNS settings ensure SSL certificates function properly, maintaining the integrity of corporate communications and online presence.

Financial Institutions

• Security Compliance: For banks or financial institutions, SSL certificates are required to meet regulatory standards. DNS errors causing SSL mismatches can result in regulatory fines and loss of user trust.
• DNS Management: Proper DNS configuration is essential for uninterrupted service and the secure transmission of sensitive financial data.

SaaS Platforms

• User Trust: SaaS applications rely on SSL certificates for secure communication. DNS misconfigurations leading to SSL errors can disrupt service and erode trust.
• Consistency: Ensuring the DNS records point to the correct server during updates or migrations helps maintain security and seamless user experience.

Content Delivery Networks (CDNs)

• Global Service Delivery: SSL certificates ensure that CDN services deliver secure, encrypted content to users. Incorrect DNS settings can break secure connections, leading to service failure.
• Optimization: Ensuring DNS accuracy ensures CDN-backed services continue to deliver content securely across global nodes.

Web Hosting Providers

• SSL Provisioning: Web hosts manage SSL certificates for clients. DNS issues during certificate provisioning or migration can affect all client domains.
• Service Reliability: Accurate DNS and SSL configuration are essential for maintaining the reliability and security of hosted sites.

Cloud-Based Applications

• Security Assurance: Cloud services depend on DNS and SSL for secure communication between end-users and services. DNS errors can break secure connections, leading to system vulnerabilities.
• DNS Accuracy: Proper DNS setup ensures SSL certificates serve as intended, maintaining encryption across cloud-based applications.

Common Technical Issues with SSL Certificate Errors Due to DNS Misconfigurations

SSL Certificate Mismatch Error

• Description: Occurs when the domain name on the SSL certificate doesn't match the domain name being accessed by the user.
• Cause: DNS misconfiguration such as missing subdomain records, leading to a mismatch between the SSL certificate and the domain being accessed.
• Resolution: Ensure that DNS records, especially A and CNAME records, are pointing to the correct domain that matches the SSL certificate.

SSL Certificate Not Trusted Error

• Description: This error happens when the SSL certificate is untrusted by the browser, typically because the certificate was issued by an unrecognized Certificate Authority (CA).
• Cause: DNS errors that lead to users being directed to a server with an outdated or self-signed certificate instead of the correct one.
• Resolution: Ensure the correct certificate chain is installed on the server, and that DNS records are directing users to the correct server hosting the valid certificate.

SSL/TLS Handshake Failure

• Description: A failure to establish a secure connection due to SSL/TLS configuration mismatches.
• Cause: Incorrect DNS settings causing users to connect to the wrong server or one without the correct SSL setup.
• Resolution: Verify that DNS records point to the correct server and that SSL/TLS protocols are correctly configured on the server.

Mixed Content Error

• Description: The page is loaded over HTTPS, but some elements (e.g., images, scripts) are loaded over HTTP, making the page insecure.
• Cause: DNS misrouting or server misconfiguration, which can cause mixed content issues if insecure resources are loaded from a different server.
• Resolution: Ensure all elements on the website are served over HTTPS and DNS records point to the correct server.

Incomplete SSL Certificate Chain

• Description: A partial SSL certificate chain leads to browsers not being able to validate the certificate.
• Cause: DNS issues or server misconfiguration that cause intermediate certificates to be missing, causing browsers to distrust the SSL certificate.
• Resolution: Ensure that all intermediate certificates are properly installed on the server and that DNS is configured correctly to point to the right server.

SSL Certificate Expiry

• Description: The SSL certificate has expired, leading to trust errors.
• Cause: DNS records point to a server with an outdated SSL certificate.
• Resolution: Renew the SSL certificate and update DNS records if necessary to point to the new server configuration.

Incorrect Subdomain Configuration

• Description: SSL certificates are issued for a specific subdomain (e.g., www.example.com), and DNS is misconfigured for the non-www version (or vice versa).
• Cause: Missing or incorrect CNAME records in DNS.
• Resolution: Ensure DNS records correctly map to the intended subdomain and that the SSL certificate covers both variations if necessary.

DNS TTL Issues

• Description: DNS caching issues can cause outdated records to persist, leading to SSL errors.
• Cause: TTL (Time-to-Live) values that are too high, causing DNS caches to hold onto old configurations.
• Resolution: Reduce TTL before making DNS changes to allow faster propagation of new records.

SSL Certificate Not Installed on the Correct Server

• Description: The SSL certificate is installed on the wrong server or not installed at all.
• Cause: Incorrect DNS configuration that leads users to a server without the correct SSL certificate.
• Resolution: Verify that DNS records are pointing to the correct server, and ensure that the SSL certificate is installed correctly.

Server Misconfiguration

• Description: Incorrect SSL/TLS server configurations that prevent SSL certificates from functioning properly.
• Cause: DNS errors leading users to a misconfigured server, which results in SSL handshake failures or incorrect cipher suites.
• Resolution: Review server settings for SSL/TLS configuration and ensure that SSL protocols are correctly set up.

Technical FAQ for Resolving SSL Certificate Errors Caused by DNS

Why am I seeing an SSL certificate mismatch error?

This error occurs when the domain name you're accessing doesn't match the domain on the SSL certificate. It’s often caused by incorrect DNS records or server misconfiguration. Ensure that DNS is pointing to the correct server with the appropriate SSL certificate for the domain.

How can DNS cause an SSL certificate not trusted error?

If DNS records direct users to a server that is not properly configured with the correct SSL certificate or if the certificate is self-signed, the browser will display this error. Make sure your DNS points to the right server, and that the server has a valid SSL certificate installed.

What is the cause of an SSL/TLS handshake failure?

An SSL/TLS handshake failure can occur when the client and server cannot establish a secure connection. DNS issues, such as misconfigured A or CNAME records, can cause users to connect to the wrong server, which leads to a handshake failure.

How do I fix mixed content errors caused by DNS issues?

Mixed content errors happen when parts of your site are loaded over HTTP while others are loaded over HTTPS. DNS issues can cause some content to be served from an insecure server. Ensure all elements on your site are loaded over HTTPS and that DNS records point to the correct server.

What should I do if the SSL certificate chain is incomplete?

An incomplete certificate chain means that intermediate certificates are missing, causing browsers to distrust the SSL certificate. Ensure that the entire certificate chain is installed on your server, and verify that DNS records direct users to the correct server with the complete chain.

How do I check if my SSL certificate has expired?

If your SSL certificate has expired, you will see an error in the browser indicating that the certificate is no longer valid. Check the expiration date using tools like SSL Labs' SSL Test or check directly through your server’s SSL settings.

Can DNS affect the subdomain configuration for SSL?

Yes, DNS can affect subdomain configurations. If DNS records for a subdomain are incorrect or missing, users may be directed to the wrong server or face certificate mismatch issues. Ensure DNS records are configured for both www and non-www subdomains if necessary.

How do I resolve DNS TTL caching issues after DNS changes?

TTL values determine how long DNS records are cached by resolvers. If the TTL is too high, old records can persist, causing SSL issues. Before making DNS changes, lower the TTL to allow faster propagation. After the migration, you can increase the TTL again.

What is the best way to check if my SSL certificate is installed correctly?

You can use online tools like SSL Labs' SSL Test to check the installation of your SSL certificate. These tools will tell you if the certificate is correctly installed and if the full certificate chain is complete.

How can I prevent SSL issues caused by DNS in the future?

• Always ensure your DNS records are accurate and point to the correct server.
• Keep your SSL certificates up to date and installed on the correct server.
• Regularly test DNS propagation and SSL certificate validity.
• Use a DNS provider with low TTL values to reduce propagation time when updates are needed.