Whenever we easily enter a website address in the browser’s address bar, such as… www.example.comAnd the moment we see the web page content, a sophisticated and efficient global collaboration is taking place in the background. This behind-the-scenes process, orchestrated by the “Domain Name System” (DNS), converts the domain names that we are familiar with and easy for humans to remember into digital addresses that machines can understand. This process is known as domain name resolution, and it is the cornerstone of the smooth operation of the internet.
What are domain names and domain name resolution?
A domain name can be considered like a property address on the internet, while an IP address represents its precise geographical coordinates. The Domain Name System (DNS) acts as a vast distributed database, and its primary function is to maintain the mapping relationship between domain names and IP addresses.
Domain name resolution is essentially a query process. When you visit a website, your device doesn’t know the actual IP address of that website.www.example.comWhere is the corresponding server located? It must query the DNS to obtain the IP address associated with that domain name (for example).93.184.216.34In order to establish a connection with the target server and retrieve web page data, this process is necessary. Without it, the internet would revert to its primitive state, where users would have to memorize complex strings of numbers.
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The hierarchical structure and composition of the Domain Name System (DNS)
DNS is not a centralized server; rather, it is a hierarchical, distributed naming system. Understanding its structure is crucial for comprehending the resolution process.
root name server
This represents the highest point in the entire DNS hierarchy. There are 13 logical root server clusters worldwide (with hundreds of physical nodes distributed across various locations). These root servers do not directly resolve specific domain names; instead, they are responsible for providing the addresses of the top-level domain servers. You can think of them as a large telephone directory that helps you find the appropriate section for a particular country or category.
Top-level domain server
TLD (Top-Level Domain) servers are responsible for managing specific top-level domains, for example….com、.org、.netCommon top-level domains, as well as....cn、.ukTop-level domains for country and region codes. When a query request is received, it provides the addresses of the authoritative domain name servers that manage that domain name.
Authoritative Domain Name Servers
This is the “terminal station” for domain name resolution. For each domain name that is registered, its owner specifies a set of authoritative DNS servers (usually provided by the domain name registrar or a third-party DNS service provider). These servers store the most authoritative and up-to-date records for that domain name.A记录(IPV4 address),AAAA记录(IPV6 address), etc. When the query reaches this point, the exact IP address will be provided as the answer.
recursive parser
This is a “local guide” for direct communication between user devices, which is typically provided by your internet service provider or a public DNS service provider (such as…)8.8.8.8It is used for operations. It does not store fixed domain name records, but it is responsible for representing users in the entire process of conducting complex queries. It starts from the root level and asks questions layer by layer until it obtains an answer from an authoritative server. The results are then cached and returned to the user.
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The complete process of domain name resolution
Let’s follow a complete parsing request to uncover every step from the input to the acquisition of the IP address.
Step 1: Initiate a query and perform a local search.
When you enter a domain name in your browser and press Enter, the operating system first checks the local DNS cache, which includes both the browser’s cache and the operating system’s cache. If the domain name has been accessed before and the cache is still valid, the IP address is returned immediately, and the resolution process is completed at this point. This is referred to as a “non-recursive query.”
If no local records are available, the operating system will send the query request to a pre-configured recursive resolver.
Step 2: Iterative query using the recursive parser
After receiving a request, the recursive parser also checks its own cache first. If there is no cache available, it acts as the user’s agent and begins a process of “iterative querying”.
It will first contact one of the 13 root domain name servers (whose addresses are usually hardcoded in the resolver software). The root servers do not provide the final answer; instead, they determine the appropriate server based on the domain name’s suffix (for example….com), and reply with the list of TLD server addresses responsible for that top-level domain.
Step 3: Querying top-level domains and authoritative servers
The recursive parser then proceeds to contact one of the TLD (Top-Level Domain) servers (for example….comThe server sends a query. The TLD (Top-Level Domain) server then examines the next part of the request (for example…example), and reply to the person in charge.example.comThe address of the authoritative domain name server for this domain.
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Step 4: Retrieve the final record and return it.
Finally, the recursive resolver sends a query to the authoritative domain name server. The authoritative server looks up the information in its zone file.www.example.comThe correspondingA记录OrCNAME记录And return the final IP address to the recursive resolver.
After receiving the IP address, the recursive parser stores it in its own cache for a certain period of time (following the TTL value of the record) for use by other users in subsequent queries. At the same time, it returns the final result to the user's operating system.
Step 5: Establish a connection
The user's operating system provides the IP address to the browser, which then uses this IP address to establish a TCP connection with the target web server. The browser sends an HTTP request, and ultimately, the web page is loaded.
Analysis of the core DNS record types
The DNS database stores various types of records, each with its specific purpose.
A记录This is the most basic form of record; it directly maps a domain name to an IPv4 address. For example,www.example.comTheA记录Yes93.184.216.34。
AAAA记录YesA记录The IPv6 version is used to direct a domain name to an IPv6 address.
CNAME记录It’s an alias record. It allows you to map one domain name to another domain name, rather than to an IP address. For example, to…www.example.comSet it tohost.example.comTheCNAMESo, the query...wwwAt that time, the parser needs to perform another query.hostTheA记录This provides flexibility for management, but it will incur an additional overhead in terms of the number of queries that need to be executed.
MX记录This is used to specify the email server address that receives emails for that domain name. When sending an email, the sender's email server queries the target domain name to determine which server should be used for delivering the email.MX记录It comes to find the delivery destination.
TXT记录It is commonly used to store some text information, and its most common applications are implementing SPF (Anti-Spam Policy) and domain name ownership verification.
NS记录Indicating which authoritative DNS server manages the domain name’s resolution records is crucial for the delegation of DNS hierarchy.
DNS Security and Optimization
DNS was not designed with security in mind from the beginning, which has led to various issues and the development of corresponding optimization solutions.
DNS hijacking is a type of attack where attackers manipulate DNS responses to redirect users to malicious websites.DNSSECIt emerged in response to the need for enhanced security. It verifies DNS data using digital signatures to ensure that responses have not been tampered with and come from legitimate, authoritative servers, thereby providing source authentication and data integrity.
In order to improve parsing speed and reduce the load on upstream servers, caching mechanisms are ubiquitous. From browsers and operating systems to recursive resolvers, DNS records are cached. Each record comes with additional information…TTLThe value determines the validity period of the cache.
Public DNS services such as…8.8.8.8、1.1.1.1They not only offer faster parsing speeds and higher stability but also generally possess better security features, capable of filtering out malicious websites. As such, they have become a popular choice for many users looking to optimize their online experience.
summarize
Domain name resolution is a complex yet highly efficient process of distributed system collaboration. It seamlessly converts human-readable domain names into IP addresses that machines can recognize, and it is an essential first step in any internet access. The process involves servers ranging from the root servers to the authoritative name servers…A记录toMX记录From recursive queries to caching mechanisms, every component works in perfect harmony to ensure the smooth operation of the global internet. Understanding the principles behind these processes not only helps us troubleshoot network issues but also allows us to appreciate the ingenuity and stability of the internet infrastructure.
FAQ Frequently Asked Questions
Why does it take time to take effect globally after modifying DNS records?
This is because DNS records are cached at various levels around the world. The TTL (Time To Live) value you set determines how long the record will remain in the cache of recursive resolvers. Until the TTL expires, users around the world may still access the outdated cached record. Typically, you need to wait for the global caches to be gradually refreshed before the changes take full effect.
What is DNS pollution, and how to deal with it?
DNS poisoning refers to the practice where certain intermediate nodes (such as some internet service providers or firewalls) deliberately return incorrect DNS resolution results, preventing users from accessing specific websites or directing them to incorrect addresses. Solutions include using public DNS services that support encryption, or making corresponding configurations to protect against such attacks.DNSSEC、DNS over HTTPS/TLSTechnologies such as these are used to encrypt DNS queries in order to prevent tampering.
Which is faster: public DNS or the DNS provided by your local ISP?
This is not absolute. The DNS provided by your local ISP is usually physically closer to your device, which theoretically results in lower latency. However, public DNS services have a larger network of global servers, more optimized caching mechanisms, and cleaner caches (free from intrusive advertisements), which can lead to better overall performance and reliability. The best approach is to use tools to test the response times of different DNS providers and choose the one that suits your needs the best.
What is the main difference between a CNAME record and an A record?
The most fundamental difference lies in the target that is being addressed.A记录Directing a domain name to an IP address is the final step in the resolution process.CNAME记录To point a domain name to another domain name, the resolver needs to continue querying the system for the information related to the second domain name.A记录Only then can an IP address be obtained; it serves as an alias or a redirection target. In terms of management…CNAMEMore flexible, but it will result in a slight decrease in performance.
How to query all DNS records for a domain name?
You can use thedigOrnslookupUse command-line tools to perform queries. For example, enter the following command in the command line: dig example.com ANY It is possible to request all available records for a particular domain name. Additionally, many online DNS query websites offer intuitive interfaces that make it easy for users to view various types of record information for that domain name.
What's next, what's next?
Extended reading and practical knowledge
The following are related to the topic of this article and are suitable for further in-depth reading. Prioritize starting with the article that is closest to your current problem, and gradually expanding to surrounding topics usually works better.
- Starting from scratch: A step-by-step guide on how to efficiently apply for and configure a personal website domain name
- What is a domain name? A comprehensive guide for beginners to experts, from registration to resolution.
- A detailed explanation of the entire domain name resolution process: from entering a website address to the behind-the-scenes journey of loading the web page
- What is a domain name? A comprehensive explanation of its definition, types, and common questions.
- Domain Name Resolution and DNS Configuration: A Comprehensive Guide from Beginner to Expert
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