DNS (Domain Name System), as a core component of the internet infrastructure, plays a crucial role in translating domain names into IP addresses. However, the increasing severity of DNS poisoning has posed unprecedented challenges to normal website access. DNS poisoning, as the name suggests, refers to the malicious modification or interference of DNS query results, preventing users from correctly accessing target websites and potentially redirecting them to malicious sites. This not only affects user experience but can also expose websites to security risks. Therefore, the ability to quickly recover from website access failures caused by DNS poisoning has become an essential skill for website administrators.

　　The Principles and Common Manifestations of DNS Poisoning:

　　DNS poisoning is typically caused by DNS cache poisoning, DNS tampering, or DNS hijacking. Attackers manipulate DNS responses to redirect the domain name resolution results of target websites to incorrect IP addresses, preventing legitimate domain names from resolving to the correct servers. When DNS poisoning occurs, visitors are incorrectly redirected to an irrelevant or malicious IP address, thus preventing them from accessing the original website.

　　Common DNS poisoning problems typically manifest as:

　　Inability to resolve domain names when accessing specific websites, or resolution results pointing to incorrect IP addresses.

　　Website access becomes abnormally slow, or users experience repeated redirects or 404 errors.

　　Users cannot access the poisoned domain name, but can access the website by directly entering the IP address.

　　DNS poisoning not only prevents users from accessing the website but can also affect its SEO ranking, reputation, and user trust. Therefore, restoring normal website access is a top priority for every website administrator.

　　Causes of DNS Poisoning:

　　DNS poisoning is typically caused by the following reasons:

　　DNS Cache Poisoning: Attackers inject forged DNS records into DNS servers, tampering with normal DNS resolution records, causing users to query incorrect IP addresses. This type of attack usually targets security vulnerabilities in DNS servers.

　　DNS Hijacking: Some Internet Service Providers (ISPs) or malware manufacturers may tamper with DNS resolution results, redirecting user requests to domains or IP addresses controlled by attackers.

　　ISP or Firewall Blocking: Network operators in some regions or countries may intentionally poison or block DNS resolution due to policy or censorship needs, thereby restricting or blocking access to specific websites.

　　Quickly Recover from DNS Poisoning-Induced Access Failures

　　When a website is attacked by DNS poisoning, restoring normal access often involves the following steps:

　　1. Check DNS Resolution Records

　　First, the website administrator should check the domain's DNS resolution records to ensure they haven't been tampered with. This can be done using common DNS lookup tools, such as nslookup or dig, to query the domain's A records, CNAME records, etc., to confirm that the domain name resolution is correct.

　　Example:

nslookup example.com

　　Alternatively, use the `dig` command:

dig example.com

　　If the query results do not match expectations (e.g., pointing to the wrong IP address), it indicates that the DNS record has indeed been poisoned.

　　2. Change the DNS Server

　　If the DNS record is poisoned, the first step is to check and change your local DNS server. Usually, you can choose a public DNS service for queries, which can help bypass your ISP's DNS poisoning.

　　The steps to change your local DNS server are as follows:

　　Open network settings and change the DNS server address to a public DNS address.

　　For Linux and macOS users, you can modify the DNS configuration by editing the `/etc/resolv.conf` file.

sudo nano /etc/resolv.conf

　　Add the following content:

nameserver 8.8.8.8
nameserver 1.1.1.1

　　For Windows users, the DNS server address can be manually set in the network connection properties.

　　3. Utilize DNS Poisoning Protection Services

　　To prevent long-term damage from DNS poisoning, website administrators can choose to use DNS poisoning protection services. Many DNS service providers offer robust DNS protection features that effectively prevent DNS poisoning and hijacking. Through these services, DNS queries are transmitted via encrypted tunnels, avoiding the risk of DNS poisoning.

　　4. Enable DNSSEC

　　DNSSEC (DNS Security Extensions) is a security protocol used to protect the DNS resolution process, preventing DNS data from being tampered with. Enabling DNSSEC adds a signature verification step to the DNS resolution process, ensuring that the returned DNS response is trustworthy and cannot be tampered with by attackers. With DNSSEC enabled, the website's DNS resolution process will be more secure; even in the event of a DNS poisoning attack, the DNSSEC verification mechanism ensures that users are accessing the correct server.

　　5. Adjust Domain TTL Values

　　When DNS poisoning occurs, the caching time of DNS records can be shortened by adjusting the domain's TTL (Time to Live) value. A shorter TTL value means a shorter cache time for DNS records. This means that when DNS records are poisoned, the DNS cache expires faster, allowing for quicker recovery of normal resolution. For example, setting the TTL value to 300 seconds (5 minutes) ensures frequent DNS cache refresh, reducing the impact of DNS poisoning.

　　6. Utilizing CDN Acceleration and Load Balancing

　　To prevent single points of failure due to DNS poisoning, website traffic can be accelerated through a CDN (Content Delivery Network). CDNs not only improve website access speed but also effectively prevent DNS poisoning and DDoS attacks. Many CDN providers offer DNS resolution capabilities and support intelligent routing to help bypass DNS poisoning. Furthermore, configuring load balancers to distribute traffic across different servers can further improve website availability and protection. Even if some DNS servers are poisoned, others can continue to provide normal service.

　　DNS poisoning is a significant factor affecting website stability and security. While DNS poisoning can cause website access failures, website administrators can effectively address and restore normal access through rapid diagnostic and recovery measures. Changing DNS servers, enabling DNSSEC, using public DNS, and protecting against DDoS attacks can help reduce the impact of DNS poisoning. By continuously monitoring and optimizing DNS settings, websites can improve their resistance to poisoning, ensuring rapid recovery and maintaining stable user access when facing DNS poisoning attacks.