DNS acts as the internet's "phone book." When you visit a website, the system first queries the DNS server for the corresponding IP address. If this query result is intentionally tampered with, incorrectly redirected, or intercepted and modified, it creates what we commonly call "DNS pollution." Essentially, your DNS query is "poisoned," preventing your device from finding the website's true target server.

　　The main manifestations of DNS pollution include: websites being inaccessible or timing out, domain names resolving to non-existent IP addresses, being redirected to advertisements, blank pages, or incorrect sites, accessibility only on some devices, and problems only occurring with certain network operators.

　　How to determine if a website is inaccessible due to DNS pollution?

　　Before taking remedial measures, users can determine if it's a DNS problem through the following methods:

　　1. The same domain name yields different results on different devices. For example, access times out on a computer, but a mobile hotspot works.

　　2. Access is possible using the IP address, but domain name access fails. You might obtain the IP address via ping and access it successfully, indicating a DNS anomaly.

　　3. Access is restored immediately after changing the DNS; this is the most direct verification method.

　　4. Use nslookup or dig to check the resolution results. If the result is an incorrect IP address or resolution failure, it is highly suspected to be DNS poisoning.

　　Once the problem is confirmed to be caused by DNS, you can begin taking remedial measures.

　　Three Simple Steps to Solve DNS Poisoning Problems (Highly Recommended, Fastest)

　　Regardless of the user's technical skill level, the following three steps can solve website inaccessibility caused by DNS poisoning in most cases. The steps are from easy to difficult and can be performed in order.

　　Step 1: Switch to a Trusted Public DNS (Fastest, Most Effective)

　　Many DNS poisoning problems can be completely solved simply by changing the DNS. Public DNS servers are usually maintained by large international technology companies, offering fast resolution speeds, high security, and strong global compatibility.

　　How to change DNS in Windows:

　　Control Panel → Network and Sharing Center → Change adapter settings → WiFi/Ethernet properties → IPv4 → Set the DNS address above.

　　macOS DNS Change Instructions:

　　System Settings → Network → WiFi → Details → DNS → Add New DNS.

　　Mobile (iOS/Android) DNS Change Instructions:

　　Turn on WiFi → Tap the connected network → Configure DNS → Manual → Enter a public DNS.

　　After changing the DNS, access should usually be restored immediately. If you still cannot access the network, please continue to the next step.

　　Step Two: Refresh Local DNS Cache (Clear Old Cache Records)

　　Your device caches DNS resolution results. If the cache already records "poisoned addresses," even if you have changed the DNS, you may still be unable to access the network due to the old cache.

　　You can refresh the cache in the following ways:

　　Windows：

ipconfig /flushdns

　　macOS：

sudo dscacheutil -flushcache
sudo killall -HUP mDNSResponder

　　Android:

　　Turn Airplane Mode on and then off to refresh the DNS.

　　iOS:

　　Restart your device or switch hotspots/Wi-Fi networks to refresh.

　　Clear your cache and try accessing the website again. If the problem persists, please continue to step three.

　　Step 3: Use Encrypted DNS or Overseas Lines (Completely Bypass Pollution)

　　If the target website itself is strictly blocked or its DNS is deeply polluted, ordinary DNS replacement may not fully restore it. In this case, it is recommended that you use encrypted resolution methods, such as:

　　1. Enable DNS over HTTPS (DoH)

　　DoH can prevent ISPs or intermediate networks from modifying your DNS queries. Browsers such as Chrome, Firefox, and Edge all support enabling DoH in their settings.

　　2. Use Overseas Proxy to Resolve Domain Names

　　When DNS pollution originates from upstream in the network and is not local to the device, using overseas lines can directly bypass the polluted environment. Many high-quality proxies have built-in private encrypted DNS, which can solve both resolution and access speed issues.

　　Why does DNS pollution occur so frequently? Analysis of the underlying reasons

　　Overall, DNS pollution mainly comes from two levels: First, cross-border access leads to the interception or forgery of DNS queries. Some overseas websites, due to policies, regional restrictions, or network security mechanisms, may be blocked by certain network nodes, resulting in incorrect resolution structures. The second issue is unstable or insecure DNS servers. Some ISPs have long-running DNS caches that update slowly, and may even be vulnerable to malicious attacks.

　　DNS poisoning occurs when conflicts arise between the network environment and the service provider. Therefore, choosing high-quality DNS servers and stable internet connections is crucial.

　　FAQs:

　　1. Will changing my DNS affect my network speed?

　　A: Yes, but usually with a positive impact. A high-quality DNS helps speed up domain name resolution, thus improving webpage loading speed.

　　2. Is it safe to change to a public DNS?

　　A: Yes. Providers like Google and Cloudflare have top-tier protection mechanisms and promise not to log private data.

　　3. Can I set multiple DNS servers simultaneously?

　　A: Yes. Usually, setting a "primary DNS + secondary DNS" will automatically switch, increasing stability.

　　4. Why can I access the same website at work but not at home?

　　A: This could be due to different DNS routing policies on different networks, or it could be that DNS pollution is more severe on your home broadband.

　　Summary: When you encounter website inaccessibility, resolution errors, or loading problems, it's highly likely that your DNS has been poisoned. Using the methods above, most website access problems caused by DNS resolution can be resolved within minutes. If you want to further improve access stability, you can also strengthen your network environment by combining DoH (Domain Hack), private DNS, and firewall optimization.