Domain name resolution is essentially a "translation" process. Servers on the internet can only communicate with each other using IP addresses, which are strings of numbers and inconvenient for humans to remember. This led to the development of the Domain Name System, or DNS. The role of DNS is to translate easily remembered domain names into IP addresses that computers can recognize. You can think of DNS as a "phone book" on the internet; domain names are names, and IP addresses are phone numbers.
When you enter a domain name into your browser and access it, the resolution process doesn't directly query a single server. Instead, it's completed step-by-step through a series of hierarchical and specialized DNS servers. The entire process can be roughly divided into several key stages, each interconnected.
First, your local device's cache comes into play. After you access a domain name, the operating system or browser saves the resolution results locally for a period of time. If you access the same domain name again within this period, the system will directly use the cached IP address without initiating a new query. This step exists to speed up access and reduce the load on DNS servers. For beginners, this is a major reason why sometimes after changing domain name resolution, they find themselves accessing the old website.
If the corresponding record is not found in the local cache, or the cache has expired, the device will send the request to the local DNS server. This local DNS is usually automatically assigned by your network operator, or it may be a public DNS that you manually set. It's not the final place where all domain name resolution results are stored; it acts more like a "proxy," responsible for continuing to query external domains on your behalf.
When the local DNS server receives a query request, it first checks its cache. If it has already resolved the domain name for other users and the record is still valid, it will directly return the result to you, and the process ends there. This is why, on the same network, some websites load slowly the first time, but subsequent accesses are significantly faster.
If the local DNS server also does not have a relevant record, it will begin querying higher-level DNS servers. The resolution process then enters the true "step-by-step lookup" phase.
The first stop is the root DNS server. The root server is not responsible for the IP resolution of specific domain names; its role is more like a master directory. It tells the local DNS: "Which top-level name server is responsible for this domain name?" For example, .com, .net, and .cn are each handled by different top-level name servers (TLDs). The root server doesn't return an IP address, but rather the address to query next.
Next, the local DNS will query the corresponding TLD. The TLD also won't directly provide the final IP address; it will only tell the local DNS, "Which authoritative DNS server is responsible for this specific domain name?" This further narrows down the search scope.
Subsequently, the local DNS will send a request to the domain's authoritative DNS server. The authoritative DNS server is where the domain name resolution records are actually stored; it's maintained by the domain registrar or the user-designated DNS service provider. It stores information such as A records and CNAME records corresponding to the domain name. When the authoritative DNS receives the request, it returns the final resolution result, which is the server's IP address.
After obtaining this IP address, the local DNS will both return the result to your device and cache it for a period of time according to the TTL setting for reuse in subsequent requests. At this point, the domain name resolution phase is complete, and the browser finally knows which server to connect to.
It's important to note that many beginners mistakenly believe that "domain names resolve directly to the server," but in reality, there may be multiple "redirects" involved. For example, when using a CDN, the authoritative DNS returns the address of the CDN node, not the origin server IP. The browser first accesses the CDN node, and then the CDN node accesses the actual server. This is why enabling a CDN significantly improves website speed and stability.
In practical applications, the type of DNS record directly affects the resolution result. The most common is the A record, which points a domain name directly to an IPv4 address; if using IPv6, the AAAA record is used. A CNAME record is used to set an alias for a domain name, making it point to another domain name instead of a direct IP address. For beginners, simply remembering that an A record "directly connects to an IP" and a CNAME record "points to another domain name" is sufficient for most scenarios.
After understanding the resolution process, reviewing common questions becomes much clearer. For example, why can some people access the site while others cannot after modifying the DNS records? This is because different levels of DNS caches have not yet expired. Why can I access a website using its IP address but not its domain name? This is often due to an incorrect authoritative DNS resolution configuration or a failure to refresh the local DNS cache. Why are there access problems after connecting to a CDN? It might be that the DNS record type or the pointed address does not meet the CDN's requirements.
From a holistic perspective, resolving a domain name to a server IP address is not a simple "point-to-point" process, but a system comprised of caching mechanisms, hierarchical queries, and authoritative management. It is this design that allows the internet to operate efficiently and stably despite its massive scale.
For novice website owners, what they truly need to master is not all the underlying technical details, but rather a clear overall understanding of the resolution process. If you know that the request starts locally, finds the authoritative DNS step by step, and then returns the IP address, you can quickly determine where the problem likely occurs when you encounter it.
In short, domain name resolution is the first gate to website access. No matter how powerful the server or how sophisticated the website program, if this gate cannot be opened, all efforts are meaningless. Understanding how a domain name resolves to a server IP address is not only basic knowledge but also a crucial prerequisite for the stable operation of a website. Once you truly understand this DNS resolution process, many seemingly complex website access problems will become traceable and solvable.
