In practice, we often encounter domain name resolution failures. After users enter a domain name, websites fail to open, emails cannot be sent or received, and CDN resources load abnormally. These issues may be caused by DNS resolution malfunctions. For webmasters and businesses, this not only affects the user experience but can also cause business interruptions. So, how can we troubleshoot and resolve DNS domain name resolution failures?

　　I. Common Symptoms of DNS Domain Name Resolution Failures

　　1. Domain Name Unreachable: After entering a URL, the browser displays "Cannot Find Server Address" or "DNS_PROBE_FINISHED_NXDOMAIN."

　　2. Access Failure in Certain Regions: Access works correctly in some cities or on carrier networks, but not in others.

　　3. Email Sending and Receiving Anomalies: Even after configuring a corporate email account, external email delivery fails.

　　4. CDN or Third-Party Service Anomalies: Even after connecting to a CDN or cloud service, resolution fails, and users cannot access the correct node.

　　5. Significant Resolution Delays: Modifying the resolution record may not take effect after several hours.

　　Ⅱ. Common Causes of DNS Resolution Failure

　　1. DNS Cache Not Updated: The DNS system has multiple levels of cache, including on the local computer, router, and carrier DNS servers. After modifying records, these caches may still retain old resolution results, preventing some users from accessing them immediately.

　　2. Improper TTL Value: The TTL value determines how long the resolution result is cached. If the TTL is too long (e.g., 24 hours), changes to the resolution will need to wait for the cache to expire before they take effect.

　　3. Record Configuration Errors: Common configuration errors include incorrect IP addresses in A records, circular or conflicting CNAME entries, MX records not pointing to the correct domain name, and duplicate configuration leading to resolution failures.

　　4. Incomplete Domain Name Registration or Abnormal Status: In China, an unregistered domain name may result in website blocking. Expired, locked, or inactive domain names can also cause resolution failures.

　　5. DNS Service Provider Issues: If the DNS service provider's servers are down or synchronization is delayed, resolution records cannot be delivered correctly.

　　6. Global Synchronization Delay: DNS changes require synchronization with servers around the world, typically taking several minutes to 24 hours, and even up to 48 hours in some regions.

　　7. Network or Local Environment Issues: Common causes include the local computer's DNS cache not being cleared, the router not refreshing the cache, and the user setting an incorrect public DNS.

　　III. Solutions for Ineffective DNS Resolution

　　1. Clear the Local DNS Cache (Windows & Linux)

　　On Windows, you can use the command:

ipconfig /flushdns

　　On Mac, you can use:

sudo dscacheutil -flushcache
sudo killall -HUP mDNSResponder

　　This will clear any remaining DNS cache on your computer and retrieve the latest resolution results.

　　2. Check the TTL value and set it appropriately. If your business requires frequent IP changes, it's recommended to set the TTL to 300 seconds (5 minutes) to ensure faster updates without placing excessive pressure on the DNS server. For stable resolution records, you can set the TTL to 3600 seconds or even longer.

　　3. Carefully check the resolution records. Is the A record IP correct? Are there any circular CNAME references? Does the MX record point to the correct mail server domain? Is a CNAME configured for the root domain (root domains generally cannot use CNAMEs)?

　　4. Verify the domain name's status. Check your domain's registrar's backend to see if it's expired, frozen, or has completed real-name verification and record-filing. If the domain is inactive or expired, resolution will naturally not work.

　　5. Change or optimize your DNS provider. If your DNS provider is unstable, consider switching to a more reliable one.

　　6. Test using a public DNS server. Change your local computer's DNS to a public DNS server and test whether it resolves correctly to rule out DNS hijacking or caching by your carrier.

　　If all of these checks are correct, it's likely that the DNS records are still being synchronized. Wait patiently for a while (usually no more than 24 hours) and the problem will resolve itself.

　　IV. Preventative Measures for DNS Resolution Failure

　　Set a reasonable TTL value in advance to avoid excessive wait times when modifying records. Choose a reliable DNS service provider to ensure stable resolution and global synchronization speed. Regularly monitor resolution status to promptly identify and resolve anomalies. Test access in multiple locations to avoid misjudgments caused by testing only locally. Prepare a backup resolution solution to quickly switch to if the primary DNS service fails.

　　DNS domain name resolution failure is a common problem in website operations and maintenance. While it can manifest in a variety of ways, the underlying causes are often related to cache failure, record misconfiguration, improper TTL settings, service provider latency, or abnormal domain name status. The key approach to resolving this issue is to first flush the cache, then check the records, confirm the domain name status, test the public DNS, and finally patiently wait for synchronization. Mastering these methods will allow you to quickly identify and resolve most resolution issues.