When building a website or application, you might encounter a common problem: the same domain name resolves to different IP addresses in different regions, sometimes even making it inaccessible. This phenomenon is called DNS inconsistency. For beginners, this problem is very frustrating, as you might think, "The server is clearly working fine, so why can't I access it in some places?" In fact, this involves multiple factors, including the principles of DNS, caching mechanisms, service provider policies, and network environment. Understanding these factors allows you to address the problem specifically, rather than blindly troubleshooting the server or modifying code.

　　Why do DNS resolution results differ across regions?

　　Beginners are easily alarmed by "different resolution results," assuming it's a server problem. Actually, the main reasons for differences in DNS resolution results fall into the following categories:

　　1. Differences caused by DNS caching

　　DNS query results have a TTL (Time-To-Live) in multiple layers of caching, including local, ISP, and authoritative DNS servers. Some nodes may cache old IPs, causing some regions to still resolve to expired or outdated addresses. This is the most common reason.

　　2. Geo-Distributed DNS Strategy

　　Many large websites and cloud services use GeoDNS (Geographic DNS), returning different IP addresses or nodes based on the user's location. For example, domestic users receive domestic node IPs, and overseas users receive overseas node IPs. This strategy can speed up access, but it can also lead to seeing different resolution results in different regions. This isn't an error, but rather an intentional optimization.

　　3. Domain Provider Synchronization Delay

　　If you recently modified your domain name resolution records (e.g., updating A records or CNAME records), some DNS nodes need time to synchronize the new records. Before synchronization is complete, different regions may resolve to different results. This is a common situation for beginners where "accessible in some regions after DNS modification" occurs.

　　4. DNS Poisoning or Hijacking

　　In some countries or regions, ISPs may interfere with DNS resolution, returning incorrect IP addresses or blocking resolution. This type of problem is more likely to occur in mainland China and some overseas nodes. The manifestation is: you can ping the server, but the IP address resolved by the domain name is incorrect.

　　5. DNS Configuration Errors

　　If authoritative DNS records are misconfigured, such as an A record pointing to the wrong IP, an incorrectly set NS record, a CNAME cycle, or an error, then DNS servers in different regions may return different results or even fail to resolve DNS due to different query strategies.

　　How to Troubleshoot Inconsistent DNS Resolution?

　　For inconsistent resolution results across different regions, beginners can systematically troubleshoot using the following steps:

　　1. Use Online DNS Lookup Tools

　　For example, use tools like `dig`, `nslookup`, or online websites to query the resolution results from different nodes globally to determine whether the problem is regional or global.

　　2. Clear Local Cache

　　After modifying DNS records, first clear the local cache:

　　Windows: `ipconfig /flushdns`

　　macOS: `sudo dscacheutil -flushcache; sudo killall -HUP mDNSResponder`

　　Linux: Restart nscd or related caching services

　　Ensure that the error is not caused by the local cache.

　　3. Test ISP DNS

　　Different ISPs' DNS servers may cache different results. Try switching to a public DNS server to test and rule out ISP caching issues.

　　4. Check Authoritative DNS Configuration

　　Ensure that the records on your domain registrar and DNS service provider are correct, and that the NS records point to authoritative servers. Common errors include inconsistent NS records, excessively long TTL settings causing slow synchronization, and incorrect record format or IP address input.

　　5. Pay Attention to GeoDNS Policies

　　If using GeoDNS or load balancing provided by a cloud provider, ensure that each regional node is configured correctly. For beginners, you can first disable GeoDNS or test with a single IP address to rule out policy differences.

　　6. Check for Poisoning or Hijacking

　　In some regions, if DNS queries return abnormal IPs, it may be due to poisoning. Try using encrypted DNS, switching to a reliable public DNS server, and testing with an overseas node.

　　Solutions for Inconsistent DNS Resolution Across Different Regions:

　　1. Ensure Authoritative DNS Configuration is Correct

　　First, confirm that all records are correct and that the TTL is reasonable and not excessively long. Common practices:

　　1. Setting the A record to the server's real IP address, and the NS record to the same authoritative DNS. Set the TTL to 300-600 seconds (5-10 minutes) for quick and easy changes to take effect.

　　2. Using a Global DNS Service or CDN

　　If your users are located globally, consider using a global Anycast DNS service in conjunction with a CDN to distribute static resources to regional nodes, improving access speed and stability. Anycast DNS allows different regions to obtain the resolution result from the nearest node when accessing the same domain name, reducing the probability of inconsistent resolution across regions.

　　3. Using GeoDNS Properly

　　If you do need GeoDNS for acceleration or load balancing, ensure that the zone mapping is correct and matches your business needs. Avoid using GeoDNS for complex allocations, as this can easily lead to "cannot be resolved in some regions" issues.

　　4. Clearing the Cache and Waiting for Synchronization

　　After modifying DNS records, different DNS nodes worldwide need time to synchronize. New users can wait patiently or manually clear the cache on test nodes. Synchronization usually takes 24-48 hours.

　　5. Dealing with Pollution or Hijacking

　　For certain affected regions: Using encrypted DNS, resolving via overseas DNS nodes, or combining access with a proxy can bypass ISP interference and ensure consistent resolution.

　　Summary: Inconsistent DNS resolution results across different regions is a common but controllable problem. Understanding DNS caching, GeoDNS, ISP policies, and pollution interference will allow you to address these issues effectively. For beginners, the core ideas are:

• Ensure authoritative DNS is configured correctly
• Use global DNS services or CDNs to improve stability
• Understand caching and synchronization latency
• Perform necessary bypassing or encrypted resolution for polluted and interfering regions

　　Mastering these ideas will allow you to effectively avoid access anomalies caused by DNS resolution differences, ensuring stable operation of your website or application globally.