What is an A record? Explanation of the most common DNS resolution records.

　　The A record is the most basic and common record type in DNS resolution. For the vast majority of websites, the successful access to a server by a user entering a domain name in their browser almost always relies on the involvement of A records. Many beginners, when first encountering domain name resolution, will see a bunch of terms like A record, CNAME, MX, and TXT in the DNS console, but won't understand their functions or when to use which one. Below, we'll systematically explain what an A record is and the most common record types in DNS resolution from the easiest-to-understand perspective, using simple language to explain each concept, so even those with no prior knowledge can understand step by step.

　　Before understanding A records, it's essential to have a general understanding of DNS. The internet essentially locates servers through IP addresses. Every server on the network has a unique IP address, such as 192.0.2.1 or 2001:db8::1. However, remembering a string of numbers is both cumbersome and prone to errors, hence the existence of domain names. The role of DNS is to establish a set of rules for automatic translation between "human-readable domain names" and "machine-readable IP addresses." When you enter a domain name in your browser and press Enter, DNS helps you find the server IP address corresponding to that domain name, and then the browser establishes a connection based on that IP address.

　　An A record, short for Address Record, can be understood as an "address record." Its function is very simple and direct: to point a domain name to an IPv4 address. For example, if you have a server IP address of 203.0.113.10, and you add an A record in the DNS resolution pointing example.com to this IP address, then when a user accesses example.com, DNS will tell the user's computer: "The server address corresponding to this domain name is 203.0.113.10," and subsequent access will proceed smoothly.

　　In practical use, an A record typically contains several key elements: host record, record type, record value, and TTL (Time To Live). The host record specifies which domain or subdomain the DNS record is resolving. For example, "@" usually indicates the root domain, such as example.com itself, while "www" indicates www.example.com. The record type is A, indicating it's an IPv4 address resolution. The record value is the server's IPv4 address. TTL (Time To Live) indicates how long the DNS record can be cached; a smaller value means the change takes effect faster, but also increases the number of DNS queries.

　　Many beginners ask if an A record can only resolve one IP address. Theoretically, a domain can have multiple A records, each pointing to a different IP. This is commonly used for simple load balancing or disaster recovery scenarios. When DNS returns multiple IPs, clients typically choose one to access based on certain rules, thus distributing access pressure to some extent. However, it's important to note that DNS-level load balancing is relatively basic and cannot achieve very fine-grained traffic control.

　　Understanding the A record makes understanding other common DNS record types much easier. The most easily confused with the A record is the CNAME record. CNAME stands for Canonical Name Record. It doesn't directly point to an IP address, but rather to another domain name. You can think of a CNAME as an "alias." For example, if www.example.com uses a CNAME to point to example.com, when a user accesses www.example.com, the DNS will first find example.com, and then find the final IP address through the A record of example.com. The advantage of CNAME is its flexibility; when the IP address changes, only the A record of the target domain needs to be modified, and all CNAME records pointing to it will automatically take effect.

　　The records most closely related to website access are A records and CNAME records. In email systems, the most common record is the MX record. MX stands for Mail Exchange Record, and it specifies the address of the server that receives emails. When someone sends an email to yourname@example.com, the mail server will first query the MX record of example.com to see which server the email should be delivered to. MX records usually have priority, used to switch to a backup server when the primary server is unavailable.

　　TXT records are very common in many scenarios. Essentially, it's a DNS record that can store arbitrary text information. Initially, TXT records had few uses, but with increasing internet security needs, they have gradually taken on important tasks such as domain verification, anti-spam, and anti-spoofing verification. For example, configuring SPF, DKIM, or DMARC email security policies, or applying for SSL certificates or connecting to third-party services, may require adding a TXT record with specific content in the DNS to prove that you have administrative rights to the domain.

　　Besides these, there are AAAA records and NS records. The function of an AAAA record is similar to that of an A record, the difference being that it points to an IPv6 address. With the gradual popularization of IPv6, more and more websites will configure both A and AAAA records to be compatible with different network environments. NS records are used to specify which DNS servers will resolve the domain name; they are usually only involved when registering a domain or changing DNS service providers, and are relatively less familiar to beginners.

　　Returning to the core A record, its importance stems from its fundamental role in accessing virtually all websites. Whether you're building a personal blog, a corporate website, or deploying an API service, if your service is accessible via an IPv4 network, you'll almost always rely on A records. Even with CDNs, load balancers, or other intermediate services, at some point, the domain name will still resolve to a specific server IP address via the A record.

　　In practice, configuring A records isn't complex, but some details are easily overlooked. For example, many beginners are unsure how to fill in the host record when resolving the root domain. Most DNS providers use "@" to represent the root domain; mistakenly entering the full domain name can cause resolution failures. Furthermore, changes to A records don't take effect globally immediately because DNS has a caching mechanism, and cache refresh times vary across regions and ISPs. This explains why sometimes "it works on my end, but not on others."

　　The best way to understand DNS isn't by rote memorization, but by imagining the entire process in real-world scenarios. When you visit a domain name, DNS is like a constantly queried and cached phone book, and the A record is the most direct line of information: what number this name corresponds to. Once you understand this, you'll find that other record types are all supplementary explanations to this "phone book" in different scenarios.