Domain name pollution (DNS pollution) refers to the act of maliciously tampering with the domain name resolution results, causing users to be directed to wrong or malicious IP addresses when accessing the target domain name. Its hazards include service interruption, phishing attacks, data leakage, etc., which require accurate detection and risk avoidance through professional technical means. Let us understand the definition and hazards of domain name pollution, and then learn various detection methods including tool use and technical principles. Of course, there are some precautions that cannot be missed in this process!

1. Core detection methods and technical principles

1. Multi-source DNS resolution comparison

By comparing the resolution results of different DNS servers for the same domain name, abnormal IPs can be identified. Use public DNS (such as Google DNS `8.8.8.8`, Cloudflare DNS `1.1.1.1`) to cross-verify with local ISP DNS. If the resolution results are inconsistent (such as unconventional IPs returned locally), there is a possibility of pollution. The command line tool `nslookup` or `dig` can quickly perform verification:

dig example.com +short @8.8.8.8 # Use Google DNS query
dig example.com +short @1.1.1.1 # Use Cloudflare DNS query
```

If the difference in the returned IP exceeds the threshold (for example, 30% of the cross-border resolution results point to unconventional IPs), a deep investigation needs to be initiated.

2. Comprehensive scanning with online tools

Use professional platforms (such as DNS Checker and Sucuri SiteCheck) to perform global node detection. These tools aggregate resolution data from multiple geographic locations around the world, generate visual reports, and identify regional pollution or blacklist associations. For example, if a domain name resolves normally in Asia but returns an incorrect IP in Europe, it may be a targeted poisoning. At the same time, the tool will detect whether the domain name is marked as malicious by a security alliance (such as Google Safe Browsing) and scan the status of SSL certificates (such as the certificate issuer does not match the domain name owner).

3. In-depth analysis of network traffic

Deploy traffic monitoring tools (such as Wireshark and Suricata) to capture DNS request and response packets, and analyze key field anomalies:

Anomalies in response time: Legitimate DNS responses are usually in milliseconds, and forged responses may be significantly higher due to transmission path delays.

TTL value tampering: Attackers often modify the TTL (Time to Live) of DNS records to induce clients to cache polluted results for a long time.

Non-authoritative response: The authoritative DNS server should return the `AA` (Authoritative Answer) flag. If the response lacks this flag and the IP is abnormal, it is suspected of intermediate hijacking.

4. ICP filing and historical record tracing

For domain names that need to be filed (such as those operated in mainland China), compare the current filing number, IP and historical legal records of the domain name to be tested. If the filing number has not changed but the resolved IP has mutated, or the IP location (such as the original Shanghai data center mutated to an overseas IP) does not match, the probability of pollution is extremely high. Automated tools can crawl public ICP databases to complete real-time comparisons and reduce manual errors.

5. Actively detect the authoritative DNS chain.

The patented technical solution (such as CN104113447A) sends resolution requests to all authoritative DNS servers and local LDNS (Local DNS) of the domain name, and counts the response deviation rate. If more than 10% of the LDNS return unconventional IPs, it is determined that there is pollution. This method requires obtaining a complete NS record chain and is suitable for enterprise-level monitoring systems.

2. Operational precautions and risk avoidance.

In the pre-environment cleaning, the local DNS cache is forced to be cleared before detection. Windows executes `ipconfig /flushdns`, and Linux/Mac uses `sudo systemdresolve flushcaches`. Avoid residual polluted data from interfering with the results.

At the same time, disable browser DNS cache plug-ins (such as some accelerators) to ensure that requests go directly to the public DNS. The principle of tool cross-validation is that a single tool may have detection blind spots (such as insufficient regional node coverage).

At least two types of tools must be combined, online scanning platform (global perspective) + command line tool (real-time) + traffic analysis (bottom-level verification). When the three conclusions are consistent, the reliability of the judgment exceeds 95%.

High-defense server linkage strategy. When selecting a high-defense server, focus on verifying the attack traffic cleaning capabilities of the data center operator and the dynamic diversion mechanism of the BGP line.

The cleaning center needs to support attack traffic of more than 100Gbps and complete malicious traffic filtering in seconds to ensure the availability of ports 80/443.

When DNS pollution is accompanied by DDoS attacks, the operator should automatically switch the traffic to the high-defense IP segment to avoid business interruption.

Avoid choosing a service provider that only relies on static IP black hole blocking, as such solutions are prone to failure under complex pollution attacks.

Continuous monitoring and automated response require the establishment of a domain name health dashboard to track core indicators. Including resolution consistency, the consistency of DNS return IPs in major regions around the world (needs to be >98%). Response delay has the average delay of authoritative DNS queries (exceeding 500ms triggers an alarm). In the blacklist state, it is necessary to synchronize Spamhaus and other security alliance databases in real time. Combined with script automation processing, if pollution is detected, the backup DNS will be switched immediately, and the SSL certificate re-issuance process will be triggered.

Legal compliance and data traceability, enterprise-level detection must comply with data privacy regulations. When using WHOIS query, avoid collecting the privacy protection registrant information (such as email, phone number) of the domain name. Store detection logs for no more than 30 days, encrypt storage and restrict access rights. If a pollution incident is confirmed, immediately submit the chain of evidence to ICANN or the National Internet Emergency Center (CNCERT), including the original resolution record and the pollution IP path tracking data.

Domain name pollution detection is a systematic project that requires the integration of technical tools, architecture design and compliance management. From the rapid response of basic resolution comparison, to the attack resilience enhancement of high-defense services, to the continuous defense of automated monitoring, the rigor of each link together constitutes a pollution-immune network. Especially when choosing a high-defense server, the operator's support for BGP dynamic scheduling and cleaning center capacity will directly affect the business survival under extreme attacks.