Why is your domain "disobeying"? Let's talk about DNS pollution.

To understand poisoning, you first need to understand how domain names are converted into IP addresses. When you type "example.com" into your browser, your computer doesn't directly know where it is. It queries a "request server" called a recursive DNS server (usually provided by your ISP). If this query server doesn't know the answer, it queries upwards layer by layer until it finds the authoritative DNS server managing "example.com," retrieves the correct IP address, and returns it to you, storing this result for a short time (caching) for faster responses next time.

Poisoning occurs at this query stage. An attacker (or some network intermediary device) impersonates the authoritative server, sending a forged, incorrect IP address reply to the recursive DNS server. This forged reply arrives faster than the real reply. The recursive server, believing it to be genuine, caches this incorrect IP address and, for the next few minutes to hours, directs all users querying "example.com" to that incorrect address.

Error addresses typically fall into one of the following categories: a non-existent "black hole" IP causing connection timeouts; a link to the local loopback address `127.0.0.1` leading you to your own computer; or a malicious website filled with ads, fraudulent content, or even malware.

Where does poisoning occur: Vulnerabilities in the network path

Domain poisoning doesn't attack your website server or your users' computers. Its target is the communication trust chain between the two. The problem mainly lies in three levels.

The most common and most difficult to combat individually is policy-based poisoning by national or regional firewalls. This is to restrict access to certain overseas websites or services. When the system detects that a local user's DNS query points to a listed domain, it intervenes at key nodes in the query path (such as international gateways), preemptively returning an incorrect IP address. This type of poisoning is geographically specific, usually only effective against users in specific countries or regions.

The second type is malicious, indiscriminate network attacks. Attackers might gain control of a critical network router or use man-in-the-middle attacks to massively monitor and forge DNS responses on the public internet. Their aim could be to hijack traffic for advertising, conduct online fraud, or be part of a large-scale distributed denial-of-service (DDoS) attack. The infamous 2010 "Baidu domain hijacking" incident is a case of a global DNS cache poisoning attack.

The third type might stem from problems in the local network environment. Insecure public Wi-Fi networks, corporate routers, or even malicious internet service providers might tamper with DNS responses, redirecting users to their pre-set pages (such as inserting advertisements). In this case, the scope of the poisoning is relatively small.

A simple detection approach: Query different public DNS servers from different network environments.

On the network you suspect is poisoned, execute:

nslookup yourdomain.com

Then query a clean public DNS server (this may require using a proxy or switching networks):

nslookup yourdomain.com 8.8.8.8

Compare the returned IP addresses. If they don't match, poisoning is likely present.

Technical Characteristics and Identification Methods of Domain Pollution

Domain pollution has several distinct technical characteristics, and understanding these helps in its identification. First, there is inconsistency in responses. The same domain name, queried from different networks such as China Unicom, China Telecom, and the CERNET, or queried using different public DNS servers such as `114.114.114.114`, `8.8.8.8` (Google), and `1.1.1.1` (Cloudflare), may return drastically different IP addresses.

Second, there are anomalous TTL times. In a genuine DNS response, the authoritative server informs the recursive server how long this result can be cached (TTL, Time to Live), usually several hours or longer. Forged pollution responses, however, often have very short TTL values ​​(e.g., minutes), and the TTL returned for each query may even change randomly. This is to ensure rapid effectiveness or ineffectiveness when policies are adjusted.

Poisoning behavior typically targets port 53 of the UDP protocol. Because standard DNS queries are based on the connectionless UDP protocol, which is fast but unreliable and does not verify the identity of the other party, this provides an opportunity for forged responses. To combat this, DNS-over-TCP (DNS-over-TCP) and more advanced encrypted DNS protocols such as DNS-over-HTTPS and DNS-over-TLS have emerged.

The essence of domain name poisoning lies in the insufficient consideration of trust issues in the initial design of the internet's fundamental protocols, a flaw exposed in the complex network environment of today. It is an invisible "quick-response race" between users and websites. For ordinary users, learning to identify and mitigate risks by switching DNS and using encryption tools is an important digital survival skill. For website operators, understanding its principles and strengthening the basic security of domain names, while providing transparent guidance and alternative access solutions for affected users, is a pragmatic approach to maintaining business accessibility in the current network environment. A true solution depends on the widespread deployment of more secure next-generation network protocols (such as the universally adopted DoH/DoT and QUIC) and a consensus on the rules of cyberspace.