In website maintenance, server configuration, and cross-border network access, the terms "DNS leakage" and "DNS pollution" are often discussed together. Many novice website owners, upon first encountering these terms, wonder: are DNS leakage and DNS pollution the same thing? If not, what are the differences?

　　From the perspective of results, they do have similarities, such as abnormal website access, inconsistent resolution results, and significant differences in access performance under different network environments. However, from the perspective of principles, causes, and solutions, they are actually two completely different issues. Confusing them often leads to incorrect troubleshooting and prolonged delays in resolving the problem.

　　To understand the differences, we first need to start with the normal working process of DNS. DNS is essentially a query and response system: a client initiates a domain name query request, and the DNS server returns the corresponding IP address. An anomaly in any step of this process can lead to access problems. DNS leakage and DNS pollution are two typical anomalies occurring at different stages.

　　DNS leakage focuses on "who received the DNS request." Ideally, DNS queries should be sent to a DNS server explicitly specified by the user or server, such as a public DNS, an internal corporate DNS, or a DNS server forwarded through a proxy channel. If, due to system configuration, network policies, or software behavior, a DNS request bypasses the expected path and is sent directly to the local ISP's DNS or a third-party DNS, this is called a DNS leak. The core issue is not whether the resolution is correct, but rather that the query path has been exposed.

　　DNS poisoning, on the other hand, focuses on whether the returned results are correct. In a DNS poisoning scenario, the DNS request itself might be sent to a seemingly normal server, but during transmission or the response phase, it is tampered with by intermediate nodes, ultimately returning an incorrect IP address. This incorrect IP might point to a non-existent server, an error page, or even a malicious site. The essence of DNS poisoning is that the resolution result is interfered with manually or systematically; even if you are using the correct DNS, you may still get an incorrect answer.

　　From the actual experience of website owners, DNS leaks usually manifest as "the access path not conforming to expectations." For example, you may have configured a public DNS or accelerated DNS, but testing reveals that the actual DNS being used is still the ISP's DNS. This is particularly common in cross-border access and proxy environments. The website itself may not be inaccessible, but access speed may be slow, the DNS server selection may be inappropriate, or the DNS resolution results may vary significantly across different regions.

　　DNS poisoning, on the other hand, is more likely to manifest as "the website being completely inaccessible." For example, the domain name resolves to an obviously incorrect IP address, the browser displays a connection failure message, or the user is forcibly redirected to an irrelevant page. These problems often have clear regional or network characteristics; the same domain name resolves completely differently in different network environments.

　　In actual troubleshooting, a crucial distinction is that DNS leaks do not necessarily lead to incorrect resolution, but DNS poisoning almost always does. In other words, DNS leaks are more about "security and privacy risks + potential performance issues," while DNS poisoning is a "functional problem," directly affecting the website's usability.

　　To more intuitively distinguish between the two, some basic commands can be used for assessment. For example, execute the following command on the server or local terminal:

nslookup www.example.com

　　If the returned IP address is correct, but the displayed DNS server is not the one you expected, then this is a typical DNS leak. The resolution "results correctly," but the "process is incorrect."

　　If the returned IP address is clearly abnormal, or even completely inconsistent with the authoritative resolution you've verified, then DNS poisoning should be highly suspected. In this case, even if the DNS server address appears normal, the returned results have been corrupted.

　　For example, using the `dig` tool:

dig www.example.com

　　Focus on the `SERVER:` field and `ANSWERSECTION`.

　　If the `SERVER` field shows an anomaly, it's a sign of DNS leakage;

　　If the IP address in the `ANSWER SECTION` is clearly unreasonable, it's more likely DNS poisoning.

　　In a server environment, these two problems can coexist. For example, a DNS request might be leaked and use the ISP's DNS, which might then be poisoning the DNS, ultimately exposing the query path and returning incorrect resolution results. This is why many website owners find "DNS problems very complex" in practice, as the problem is often not caused by a single factor.

　　From a problem-solving perspective, the approaches are also significantly different. The core solution to DNS leakage is to control the DNS query path. That is, explicitly specify the DNS server to ensure that DNS requests from the system, application, and network layers all follow the same secure and controllable path. Common methods include fixing DNS configurations, enabling DoH (Domain-Oriented Hierarchy), and ensuring the proxy handles DNS requests.

　　The key to dealing with DNS poisoning is to bypass or combat the source of the erroneous resolution. This includes switching to a more reliable DNS provider, using encrypted DNS, preventing tampering by intermediate nodes, or reducing reliance on a single DNS through CDN and intelligent resolution. In some network environments, simply "changing the DNS" can immediately restore normal access; this is often a typical characteristic of DNS poisoning.

　　Understanding this distinction is especially important for novice website owners. Many people's first reaction to access anomalies is to "change the DNS," but if the root cause is a DNS leak, simply changing the DNS won't solve the problem because the request never actually used the new DNS. Conversely, if it's DNS poisoning, spending a lot of time troubleshooting the proxy or system configuration will also lead to many detours.