Every time you type an address into the browser, your computer asks a question as old as it is useful: where is that server? The answer is given by the DNS (Domain Name System), the infrastructure that converts readable names like tech.atrilit.com into numeric IP addresses. Without it, you would have to memorize strings of numbers like 192.168.0.26. It is, in practice, the internet’s phone book.
The problem it solves
Machines do not communicate by names, but by IP addresses, numbers of 32 bits (IPv4) or 128 bits (IPv6) that identify each network interface. But humans are not good at remembering numbers, and besides, the same website can change servers without its name changing. DNS acts as an abstraction layer: it separates identity (the domain) from physical location (the IP), so a site can migrate servers without the user noticing anything.
The interesting thing is that DNS is not a single computer with a giant list, but a distributed and hierarchical system, designed to withstand millions of queries per second without collapsing and without depending on a single point of failure.
A hierarchy of servers
Resolving a name follows a tree structure. At the top are the root servers: 13 sets of addresses managed by organizations such as ICANN, which do not resolve domains, but know where each TLD server (top-level domain) is, the ones for suffixes like .com, .es, .org and so on. At a lower level are the authoritative servers of each specific domain, the ones that actually know the exact IP of a name like tech.atrilit.com.
Between the user and that hierarchy sits the recursive resolver, usually your ISP’s or that of a service like Cloudflare or Google (8.8.8.8). This resolver does the heavy work: it asks the root, then the TLD, then the authoritative server, and returns the final IP. This process is called iterative resolution, because it jumps from level to level until it gets the definitive answer.
The journey of a query
Imagine you type tech.atrilit.com. Your computer first checks its local cache and that of the resolver. If there is nothing, the resolver queries the root and receives the address of the .es TLD servers. Then it asks one of those servers about syf.es and gets the IP of the authoritative server. Finally, it queries that server and receives the A record (address), which associates the name with an IPv4. All of this happens in milliseconds.
DNS does not only store IP addresses. DNS records are a language with several types: A and AAAA (IPv4 and IPv6), CNAME (alias from one domain to another), MX (the domain’s mail server), TXT (free text, used for verifications such as SPF or DKIM) and NS (the domain’s authoritative servers). Each record has a TTL (time to live), the time in seconds that resolvers can keep it cached before asking again.
Security: when trusting the phone book is dangerous
Classic DNS sends queries in plain text, which enables attacks such as DNS spoofing: an attacker who intercepts the traffic can respond with a fake IP and redirect you to a fraudulent site without you noticing. Two complementary solutions emerged to combat this. On the one hand, DNSSEC, which digitally signs the records with asymmetric cryptography to guarantee that the response comes from the legitimate server. On the other, DNS over HTTPS (DoH) and DNS over TLS (DoT), which encrypt the query between your device and the resolver, hiding it from anyone spying on the network, so the traffic travels inside an encrypted tunnel with TLS, the same protocol that protects websites.
These encryption layers explain why today your ISP can no longer see which domains you query: the query travels protected in an encrypted channel that only you and the resolver can read.
Why it matters
DNS is one of those invisible technologies that sustain the internet. It is estimated to handle tens of billions of queries daily, and its distributed design is the reason the network keeps working even when entire parts of its infrastructure fail. The next time you type a URL, remember: behind that blink there is a chain of servers that have travelled the world to tell you, in milliseconds, exactly where what you are looking for is.
