In daily website maintenance, domain name resolution failure is a frequent problem. Whether launching a new website, migrating a server, switching CDNs, or changing DNS services, you may encounter situations where the domain is inaccessible, the resolution is delayed, or the site is accessible in some regions but not others. Many website owners habitually assume it's due to DNS provider downtime, but in reality, the vast majority of resolution failures are related to DNS latency, cache not being refreshed, improper TTL settings, or local DNS cache blockage. To quickly resolve these issues, the key is to accurately pinpoint the source of the latency, rather than blindly waiting for the DNS to take effect.

　　DNS latency issues typically manifest in the following ways:

　　1. The domain can ping the old IP address but cannot resolve to the new IP address;

　　2. Some ISPs have updated their resolutions, while others are still using the old records;

　　3. Users report that the site is sometimes accessible and sometimes inaccessible;

　　4. Browsers still display the old site content;

　　5. After changing CDNs, the cache nodes still return the old origin address.

　　These phenomena may seem random, but there are underlying logics. The biggest reason why DNS records fail to take effect is often that the DNS cache is still working. Recursive DNS servers cache DNS records based on the TTL (Time-To-Live), and local systems, browsers, and even CDN edge nodes have their own caching layers. If any of these layers hasn't been refreshed, it will cause resolution delays or even errors.

　　How to quickly locate the cause of ineffective DNS resolution:

　　The most effective way to quickly locate the source of the ineffective resolution is to use tools like `dig` or `nslookup` to query the resolution results of different nodes. For example, using `dig` to query the current authoritative resolver for a domain name can directly trace the complete resolution chain. If the IP address shown in the query result is inconsistent with the one you set in the DNS console, then the problem lies in the upper-level DNS cache. If `trace` shows that the authoritative DNS has not yet returned the correct record, it means that the DNS record itself may not have been synchronized to the global DNS root nodes. This situation often occurs when DNS service providers change or domain NS records are updated.

　　To further confirm whether different regions have been updated, you can query multiple public DNS nodes. If some DNS nodes have been updated while others have not, this means that the propagation of the TTL change is still in progress, and you need to wait for each ISP to refresh its cache. If all public DNS servers return old results, it indicates that the TTL is too high, causing the global cache to not have expired. In this case, it should be checked whether the original TTL setting is too large, such as 86400 seconds (24 hours), causing the DNS records to fail to refresh in the short term.

　　Besides recursive DNS caching, local DNS caching is also a common source of latency, especially when developers frequently modify DNS records. Operating systems and browsers cache DNS records; to ensure that the resolution is updated, the local cache needs to be actively refreshed. If the resolution still doesn't work after refreshing the local cache, then the problem is not local, but at other levels of the DNS system.

　　Some site administrators overlook an important factor—CDN caching. When using acceleration services, resolution depends not only on DNS but also on CDN intelligent routing and edge node caching. If the origin IP changes but the CDN doesn't refresh, visitors will still access the old nodes, mistakenly believing it's a domain name resolution problem. In this case, the CDN console should be used to clear the DNS cache on the acceleration nodes, not just modify the DNS records.

　　Some DNS latency issues also stem from differences in cache synchronization between overseas and domestic ISPs. For example, China Mobile, China Unicom, and China Telecom have different DNS refresh frequencies, resulting in some regions updating several hours later than others. For websites relying on overseas users, some authoritative DNS servers update more frequently. Therefore, when troubleshooting, it's recommended to first check the resolution status of international DNS nodes to determine whether the problem is caused by domestic ISP cache latency or international network latency.

　　A more complex situation involves resolution latency caused by changes in the domain's NS record. The NS record is used by the top-level DNS to locate your domain's DNS hosting location. Once you change your DNS service provider, DNS servers worldwide need to re-acquire your new NS record. This process takes 24-48 hours. Therefore, during the NS change, old and new DNS services may appear mixed during resolution. You can use a command to check if the NS is propagated correctly. If the result shows a mixture of old and new NS records, it means that the resolution synchronization is not yet complete, and you need to continue waiting for the propagation to finish.

　　To reduce DNS latency issues, it is recommended to reduce the TTL before migrating your business. For example, if you plan to switch servers, you can change the TTL to 300 seconds 24 hours in advance. After the global DNS cache is refreshed, switch the IP address; this will complete the migration within minutes. After the operation, you can restore the TTL to a more stable value, such as 3600 seconds, to reduce long-term DNS query pressure.

　　Many users believe that domain name resolution failure is always a DNS server problem, but the real cause is often closer to the following: a high TTL causing cache latency, recursive DNS servers not being refreshed, local cache not being cleared, CDN cache interference, incomplete NS change propagation, browser cache blocking, or even incorrect hosts file settings. A systematic troubleshooting approach can quickly determine which layer of the problem is causing the issue, rather than blindly waiting 24 hours.

　　To further avoid resolution failures, it is recommended to use a DNS service with intelligent resolution, latency monitoring, and log analysis to detect anomalies promptly. For example, intelligent routing, weighted resolution, and automatic TTL optimization can significantly reduce resolution latency. For cross-border businesses, setting up multiple public DNS resolution nodes is also an important way to improve resolution stability.

　　Overall, domain name resolution failure is not accidental, but a network behavior affected by multiple layers of caching. To quickly pinpoint DNS latency issues, a comprehensive assessment is needed, considering factors such as recursive servers, local caching, authoritative DNS, CDN nodes, and NS propagation. Understanding the principles of DNS resolution, properly configuring TTL, and utilizing professional testing tools will enable faster and more stable website resolution, ensuring uninterrupted user access.