Solutions for DNS poisoning causing website inaccessibility

　　During website maintenance, many website owners encounter this situation: the server is running normally, and the domain name hasn't expired, but users report that "the website is inaccessible," "access is redirected to strange pages," and "access results are inconsistent across different regions." After investigation, the problem is often found to be DNS poisoning. DNS acts as the internet's "phone book," and if the resolution results are tampered with or hijacked, it directly affects the user's access path. For websites that rely on traffic and conversions, this type of problem not only affects the user experience but can also pose security and brand risks.

　　What exactly does DNS poisoning mean?

　　Simply put, the function of DNS resolution is to translate domain names into server IP addresses. When a user enters a domain name in their browser, the system sends a query request to the DNS server, and a connection is established only after the correct IP address is returned.

　　DNS poisoning refers to this "query-return" process being interfered with by a third party, causing users to receive incorrect addresses, advertising page addresses, or even phishing site IP addresses instead of the real server's IP address.

　　This poisoning can occur at multiple stages, such as the local network, ISP DNS, public DNS, and even cross-border network nodes. Interference at any layer can lead to access problems.

　　Common Manifestations of DNS Poisoning

　　In actual operation and maintenance, DNS poisoning typically presents the following typical phenomena:

　　First, the same domain name yields different results in different regions. It may open normally in some places, but in others it may show as inaccessible or redirecting abnormally.

　　Second, the server itself can be accessed directly using the IP address, but accessing the domain name fails. This is often the most obvious signal.

　　Third, the browser indicates that the domain name does not exist or that resolution failed, but the domain name shows a normal status in the background.

　　Fourth, being forcibly redirected to advertising pages, fake pages, or irrelevant websites.

　　Fifth, using different DNS servers to query the same domain name returns inconsistent IP addresses.

　　If you encounter any of the above situations, it is highly likely that you have DNS poisoning or DNS hijacking.

　　Main Causes of DNS Poisoning

　　To solve the problem, you must first understand its source. Common causes mainly include the following:

　　One is hijacking or caching errors at the ISP level. Some network environments interfere with DNS queries, especially noticeable during cross-border access.

　　Second, the local network or router may have been tampered with. Some malware modifies local DNS settings, causing all access to be redirected.

　　Third, an unstable or polluted public DNS service may be used.

　　Fourth, the domain name itself may have been attacked, such as experiencing DNS hijacking or cache poisoning.

　　Fifth, when deploying across regions, poor international link quality can cause resolution requests to be interfered with by intermediate nodes.

　　These problems combined can lead to the awkward situation of "the server is fine, but the website is inaccessible."

　　How to quickly determine if it's DNS poisoning

　　New website owners can check in the following order:

　　First, directly access the website using the server IP. If the IP can be accessed, but the domain name cannot, it's likely a DNS-related problem.

　　Then, use tools like nslookup or dig to query the domain name resolution results and compare them with the IP in the cloud provider's console. If they don't match, the resolution has been tampered with.

　　Next, switch to different DNS servers to query, such as 114, Alibaba DNS, Tencent DNS, and Google DNS, to see if the returns are consistent.

　　You can also use online multi-region DNS testing tools to check the DNS resolution status of different provinces and operators. If there are significant discrepancies, it can further confirm the scope of the pollution.

　　Finally, test access performance using different network environments (mobile data, broadband) to determine whether the problem is localized or global.

　　Practical Solutions for DNS Resolution Poisoning

　　Once the problem is identified, targeted solutions can be implemented. The following solutions are listed from easiest to most difficult; beginners can try them step by step.

　　First, switch to an authoritative DNS service provider.

　　Prioritize DNS services from mainstream domestic cloud providers, such as Alibaba Cloud DNS, Tencent Cloud DNS, and DNSPod. These services are highly stable and have stronger anti-poisoning capabilities. After modifying the domain's NS, wait for the resolution to take effect, and then retest access performance.

　　Second, enable DNSSEC or DNS resolution protection.

　　If your DNS service provider supports DNSSEC, it is recommended to enable it, which can effectively prevent cache poisoning and DNS resolution tampering. Simultaneously enable security features such as DNS locking, anti-hijacking, and anti-tampering to improve the overall protection level.

　　Third, use HTTPS + HSTS

　　While HTTPS doesn't directly prevent DNS poisoning, it can prevent users from being redirected to phishing websites. Enabling HSTS forces browsers to use encrypted connections, significantly reducing the risk of man-in-the-middle attacks.

　　Fourth, configure backup DNS records for important domains

　　Multi-line DNS resolution or smart DNS resolution can be used to route different IPs to different regions. If one line is poisoned, others can continue to provide service. Some DNS platforms also support health checks and automatic failover, which is very helpful for business continuity.

　　Fifth, deploy CDN acceleration

　　CDN nodes typically have built-in anti-hijacking capabilities and can hide the origin server's IP while optimizing cross-regional access quality. This is a cost-effective solution for frequently poisoned sites.

　　Sixth, use optimized bandwidth for cross-border business

　　If your website involves overseas or cross-border access, ordinary public network links are more prone to DNS resolution anomalies. In this case, consider using servers or dedicated networks with optimized lines to make DNS queries and access paths more stable. This is a key reason why many website owners choose Hong Kong or international nodes and combine them with optimized bandwidth.

　　Seventh, Temporary Solution: Local Hosts Binding

　　When the problem is urgent and cannot be fixed immediately, you can modify the local Hosts file to point the domain name directly to the correct IP. This should only be used as a short-term emergency solution and is not suitable for large-scale users.

　　Frequently Asked Questions

　　Q1: What is the difference between DNS poisoning and DNS hijacking?

　　A1: Strictly speaking, DNS poisoning is more of a passive interference at the network or caching layer, while DNS hijacking is usually an active attack or malicious tampering. However, for website owners, the handling methods are basically the same.

　　Q2: Does DNS poisoning mean the server has been hacked?

　　A2: Not necessarily. In most cases, the server itself is secure; the problem occurs at the resolution or network link layer.

　　Q3: Is clearing the local DNS cache helpful?

　　A3: If it's just a local cache error, it helps. But if the upstream DNS is poisoned, clearing the cache can only provide temporary relief.

　　Q4: Can free DNS be used?

　　A4: It can be used for small websites or test environments, but for production businesses, it is recommended to use DNS from mature cloud providers, as their stability and security are more guaranteed.

　　Q5: How long does it take to fix DNS poisoning issues?

　　A5: If it's just switching DNS services, it usually takes tens of minutes to several hours to recover. If it involves large-scale network poisoning, it may require CDN or line optimization.

　　Summary: DNS poisoning is a common problem encountered by many website owners, especially in cross-regional and cross-border access scenarios. It doesn't necessarily mean your website has been attacked, but is often a result of a complex network environment. By mastering the basic troubleshooting approach—starting with IP testing and DNS queries, and combining this with authoritative DNS, HTTPS, CDN, and line optimization—most problems can be effectively resolved. For long-term websites, proactively planning DNS security and network architecture is more important than reactive firefighting.