DNS is responsible for resolving domain names into corresponding IP addresses and providing users with the correct path to access websites. However, due to cross-regional networks, complex carrier environments, and certain special network policies, DNS poisoning has become one of the most common problems encountered by website owners and network administrators. DNS poisoning typically manifests as users accessing domain names being incorrectly resolved to fake, non-existent, or even malicious IP addresses, resulting in inaccessible web pages, abnormal redirects, or connection timeouts. To quickly determine if a problem stems from DNS poisoning, the most common and direct method is to use ping and dig tools for diagnosis. These tools can help analyze DNS resolution results, determine if the resolution is correct, and identify the scope of the poisoning.

　　When a DNS problem is suspected, the first step is often to use a ping request to test whether the domain name can return the correct IP address. Ping works by sending ICMP requests to the IP address corresponding to the domain name. While it doesn't prove whether a website is accessible, it can serve as a preliminary means of determining if the DNS is functioning correctly. If the IP address returned by ping is inconsistent with the website's actual server IP address, then the DNS is very likely poisoned. For example, you can enter:

ping example.com

　　If the return is similar：

Pinging example.com [123.45.67.89] with 32 bytes of data:

　　You need to verify that this IP address matches your actual server IP address. If they are completely different, and the returned IP comes from a local ISP, advertising server, LAN address, or a meaningless IP, it indicates that the DNS is highly likely poisoned. However, it's important to note that some websites deploy CDNs or reverse proxies, and the returned IP address may not equal the origin server's IP. In such cases, you cannot rely solely on ping; you need to combine it with tools like dig and nslookup to compare authoritative resolution results.

　　While ping is the most commonly used but also the least accurate testing tool, as it relies on the system DNS and is greatly affected by the network environment, you must use the dig tool to definitively determine if your DNS is poisoned. dig can directly query authoritative DNS and return detailed resolution records, making it the most widely used DNS deep diagnostic tool among network engineers worldwide. The results from dig show the actual domain name resolution, the records returned by the DNS server, TTL, and the source of the authoritative NS, information that is more authoritative than ping.

　　To determine if DNS is poisoned, the core approach of dig is to compare the resolution results of different public DNS servers. You can try the following in sequence:

dig example.com @8.8.8.8
dig example.com @1.1.1.1
dig example.com @9.9.9.9
dig example.com @223.5.5.5
dig example.com @114.114.114.114

　　If you find:

• Global public DNS resolution is consistent, but your local ISP's DNS returns errors;
• The IP address returned by DNS in a certain region is inconsistent with other regions;
• The resolution results contain obviously abnormal IP addresses, misleading redirect domains, or advertising IP addresses;

　　Then DNS pollution is very obvious.

　　A normal dig return example usually looks like this:

;; ANSWER SECTION:
example.com.   300   IN   A   93.184.216.34

　　The contaminated dig might return the following:

;; ANSWER SECTION:
example.com.   5   IN   A   203.98.77.123

　　The returned IP address is clearly not your server, but rather a fixed advertising or hijacking node. It typically has an extremely short TTL, a common characteristic of DNS poisoning.

　　Further confirmation of the pollution source can be done using the `dig +trace` command. This will resolve the DNS layer by layer from the root servers until the final result is returned, thus determining whether the poisoning occurred at an intermediate DNS forwarding node. Input:

dig +trace example.com

　　If the authoritative server returns the correct IP during the tracing process, but an abnormal resolution suddenly occurs at a certain node along the way, it indicates that the pollution occurred in the middle of the link, not at the source DNS service provider. This situation is often seen in ISP hijacking, cross-border network pollution, or intermediate cache errors.

　　Besides `dig +trace`, you can also use `dig ANY` to view all DNS records for a domain name, including NS, MX, A, TXT, etc. It can help determine if someone has tampered with critical entries in the DNS records. For example:

dig ANY example.com

　　If you encounter unfamiliar NS records, abnormal TXT information, or extra A records, this usually indicates that your DNS console has been compromised or maliciously tampered with.

　　When ping and dig show inconsistencies in DNS resolution, you can compare the formatted results to determine the location of the pollution. Generally, you can judge based on the following:

• Inconsistent resolved IP address with the real server → Highly suspected pollution
• Inconsistent resolution between different DNS providers → Suspected regional pollution
• Extremely low TTL (e.g., 5 seconds) or abnormal → Often local pollution by the ISP
• Different resolutions of the same domain name on different devices and networks → Obvious link pollution
• dig + trace shows correct authoritative server resolution but incorrect final resolution → Link-layer hijacking

　　These characteristics can help you quickly distinguish DNS poisoning from other common problems (such as ineffective DNS records, unrefreshed DNS cache, and outdated CDN cache).

　　Once DNS poisoning is confirmed, the most effective measure is to switch to a trusted global DNS provider and ensure that DNS records in the console have not been tampered with. To prevent intermediate nodes from forging resolutions, it is recommended to enable DNSSEC, allowing browsers to verify the legitimacy of resolution records. Furthermore, to block ISP hijacking, websites must enable HTTPS and HSTS. This way, even if the DNS incorrectly points the user to a fake IP, the browser will block further access because the certificate cannot be verified, preventing users from mistakenly accessing fake websites.

　　For websites heavily reliant on cross-border access, a CDN can be used to hide the origin server IP, reducing the DNS exposure surface. When a website connects to a CDN, DNS records will not directly expose the real server IP, but will instead use the CDN's CNAME, thus reducing the possibility of hijacking attacks. In addition, using a multi-region detection platform for DNS resolution monitoring and setting up automatic alert mechanisms can also help you detect problems as soon as poisoning occurs.

　　In summary, using ping and dig to diagnose DNS pollution is a simple and efficient method that can help you quickly identify resolution anomalies, pinpoint the source of pollution, and take remedial measures. With the right diagnostic methods, a robust DNS security system, and the deployment of multiple protective measures such as HTTPS, CDN, and DNSSEC, your website can maintain a stable, secure, and reliable access experience even in complex network environments.