When we type a website address into our browser's address bar and press Enter, most people only care about whether the page loads correctly, but few truly understand what's happening behind the scenes. In reality, before the webpage content is displayed, a series of intricate and orderly collaborations occur between the browser, operating system, DNS server, network devices, and the target server, with DNS resolution being the starting point of this entire process. If we compare the internet to a giant map, then DNS is like the "address indexing system" on that map, responsible for translating easily remembered domain names into IP addresses that computers can recognize.

　　The DNS resolution process begins within the browser. When you enter a complete domain name, such as www.example.com, the browser's first action isn't to immediately send a network request, but rather to perform a series of local checks. The browser checks if it has saved the IP address corresponding to this domain name; this is commonly known as the browser's DNS cache. If the website has been visited before and the cache hasn't expired, the browser can directly obtain the IP address, thus skipping numerous subsequent resolution steps. This is why some websites seem faster on subsequent visits.

　　If the browser cache doesn't find the corresponding record, the request is handed over to the operating system for processing. The operating system also maintains a DNS cache, which may come from browsers, other applications, or previous system-level resolution results. This cache plays a crucial role in Windows, Linux, and macOS. If the system cache is hit, the resolution process ends locally, and the browser directly uses the IP address to initiate subsequent connections.

　　When neither the browser nor the operating system cache can provide results, the system further checks for manually configured resolution rules locally. The most typical example is the hosts file. The hosts file allows users to manually specify the IP address corresponding to a domain name, and if a match is found, its priority is usually higher than that of an external DNS server. This is a common method used by many developers when debugging websites locally or troubleshooting domain name resolution issues.

　　If all the above local methods fail, the DNS query will finally leave your computer and enter the network. At this point, the operating system will send the resolution request to your currently configured DNS server. This DNS server is usually determined by your network environment, such as your home broadband provider's DNS, your company's internal DNS, or a public DNS service that you have manually configured. For ordinary users, this step is the first time they truly "seek external help."

　　The DNS server receiving the request is called the recursive DNS server. Its responsibility is to complete the entire query process for the user and ultimately return a definitive result. The recursive DNS server first checks if it has already cached the domain name's resolution result. If it exists in the cache and hasn't expired, it will directly return the IP address to the user. This is very common for frequently accessed websites and can significantly reduce overall resolution latency.

　　If the recursive DNS server also doesn't have a cache, it needs to query a higher-level DNS system. DNS is a typical hierarchical structure, with the root DNS servers at the top. The recursive DNS server first asks the root servers "where should I look up this domain name?" The root servers don't directly provide the IP address but instead return the address of the server responsible for that top-level domain, such as the server corresponding to .com, .net, or .cn.

　　Next, the recursive DNS server requests the top-level name server. The top-level name server also doesn't provide the final IP address but tells the recursive DNS server where the authoritative DNS server responsible for that specific domain is located. This step is like continuously narrowing the search scope, from the whole country to a city, and then to a specific street.

　　The actual resolution result only appears after the recursive DNS finds the authoritative DNS server. The authoritative DNS server holds the most accurate and original resolution records for the domain name. Based on the corresponding A record, AAAA record, or other types of records, it returns the IP address of the target server. This IP address is then cached by the recursive DNS for a period of time and simultaneously returned to your operating system.

　　Once the operating system obtains the IP address, it passes the result to the browser, thus completing the DNS resolution phase. The browser finally knows the target server's "location" on the network, and can then proceed to the actual network communication phase. The browser determines whether to use HTTP or HTTPS based on the protocol in the URL and establishes a TCP connection with the target server. If HTTPS is used, a TLS handshake is also performed to verify certificates and negotiate encryption methods.

　　After the connection is successfully established, the browser sends an HTTP request to the server, containing the access path, request method, browser information, etc. Upon receiving the request, the server processes it according to its configuration and application logic, which may involve reading static files or calling backend programs to generate dynamic pages. After processing, the server returns the response data to the browser.

　　After receiving the response data, the browser doesn't simply display it immediately. Instead, it goes through multiple steps, including parsing HTML, loading CSS, executing JavaScript, building the DOM tree, and rendering the page. Only after these steps are completed will you see the final website content on your screen. From entering the domain name to the page fully displaying, what seems like an instantaneous process actually involves close collaboration across multiple system layers.

　　Understanding the DNS resolution process is extremely helpful for website maintenance, server management, and troubleshooting network problems. Many common issues such as inaccessible websites, slow access, and abnormal behavior in certain regions are essentially related to DNS resolution. For example, unrefreshed DNS caches, incorrect authoritative DNS configurations, and abnormal recursive DNS responses all directly impact the user experience.

　　While DNS is a relatively "invisible" system in daily use, its stability and efficiency are crucial to the entire internet. Properly configuring DNS and understanding the resolution path not only helps beginners quickly grasp network basics but also allows experienced users to handle complex problems with greater ease.

　　Here are some frequently asked questions in practical use:

　　Why doesn't the website immediately take effect after changing the domain name resolution? This is because DNS resolution results are cached at multiple levels, including browser cache, system cache, and recursive DNS cache. Each layer of cache has its own expiration time. Only after the cache expires will the new resolution result be retrieved again.

　　Why does the same domain name resolve to different IPs on different networks? This is normal. Many websites use smart DNS, which returns different server IPs based on the user's region to improve access speed and stability.

　　Why can I access the website using the IP address but not the domain name? This usually indicates that the server itself is working properly, but there is a problem with DNS resolution. It could be that the domain name is not pointing to the correct server IP, or the resolution has not yet taken effect.

　　Will DNS affect website security? In reality, DNS itself is just a resolution system, but if DNS is hijacked or poisoned, it can indeed lead users to incorrect servers. Therefore, choosing a reliable DNS service, enabling HTTPS, and DNSSEC are effective ways to improve security.

　　Do ordinary users need to manually change their DNS? For most people, the DNS provided by their internet service provider (ISP) is sufficient. However, users with higher requirements for access speed, stability, or privacy can choose a reputable public DNS service, which can improve their overall internet experience in many cases.

　　By understanding the complete DNS resolution process from browser request to server response, you'll discover that the internet isn't a "mysterious black box," but rather a logically clear and hierarchical system. Once you grasp the basic principles, even when encountering problems, you can pinpoint the cause step by step, instead of being at a loss.