Understanding How DNS Servers and DNS Requests Work: A Complete Guide

The Domain Name System (DNS) is one of the most fundamental components of the modern Internet. Without it, every time you wanted to visit a website, you would have to type in its IP address — a series of numbers like 192.0.2.44 — instead of a human-readable domain like example.com.

In this article, we’ll take a deep dive into how DNS servers and DNS queries (requests) work, step by step — from the moment you type a URL in your browser to the instant a web page appears on your screen.

1. What Is DNS?

DNS stands for Domain Name System, and it acts as the phonebook of the Internet. Its main job is to translate domain names (like www.google.com) into IP addresses (like 142.250.190.78), which computers use to locate and communicate with each other.

Every device connected to the Internet — whether it’s a web server, laptop, or smartphone — has a unique IP address. DNS makes it possible for users to access these devices using easily memorable names instead of long numeric addresses.

2. The Key Components of the DNS System

The DNS system is composed of several types of servers that work together to resolve domain names into IP addresses.

2.1 DNS Resolver (Recursive Resolver)

A DNS resolver is typically provided by your Internet Service Provider (ISP) or a public service like Google DNS (8.8.8.8) or Cloudflare DNS (1.1.1.1).
It is the first server contacted when you enter a domain name in your browser.
The resolver’s task is to “resolve” the domain by finding the correct IP address — it does so by querying other DNS servers on your behalf.

2.2 Root DNS Servers

The root servers are the top of the DNS hierarchy.
They do not store IP addresses for individual domains but know where to find the Top-Level Domain (TLD) servers such as .com, .net, .org, .uk, etc.
There are 13 sets of root servers distributed globally, maintained by organizations like ICANN and Verisign.

2.3 TLD DNS Servers

The Top-Level Domain (TLD) servers manage domain extensions like .com, .org, .edu, .io, etc.
They provide information about which authoritative name server is responsible for a specific domain.

2.4 Authoritative DNS Servers

These are the final source of truth for a domain.
They store the actual DNS records (A, AAAA, MX, TXT, CNAME, etc.) for the domain name.
When the resolver finally reaches the authoritative server, it receives the correct IP address to return to the user.

3. How a DNS Query Works (Step-by-Step)

Let’s walk through the entire process of what happens when you type www.example.com into your web browser.

Step 1: Browser Cache Lookup

Your web browser first checks its own DNS cache to see if it already knows the IP address for www.example.com.
If found, it uses the cached IP immediately — skipping the rest of the DNS process.

Step 2: Operating System Cache Lookup

If the browser has no cached entry, it asks the operating system (via a system call like getaddrinfo()).
The OS maintains its own cache, typically managed by a local resolver service such as systemd-resolved or nscd.

Step 3: Query to Recursive Resolver

If the OS doesn’t have the record, it forwards the request to a recursive resolver (usually your ISP’s or a public DNS server).
Examples:

• Google DNS → 8.8.8.8
• Cloudflare DNS → 1.1.1.1
• OpenDNS → 208.67.222.222

Step 4: Root Server Lookup

The recursive resolver checks its cache. If it doesn’t have the record, it sends a query to one of the root DNS servers.
The root server doesn’t know the IP of www.example.com, but it responds with the address of the .com TLD DNS server.

Step 5: TLD Server Lookup

The resolver then queries the .com TLD server, asking where to find example.com.
The TLD server replies with the address of the authoritative DNS server for example.com.

Step 6: Authoritative DNS Server Lookup

Finally, the resolver queries the authoritative DNS server for example.com.
The authoritative server responds with the A record, which contains the IP address (e.g., 93.184.216.34).

Step 7: Response Returned to the Client

The recursive resolver returns this IP address to your operating system, which passes it to your browser.
The browser can now initiate a TCP/IP connection to that IP and load the website.

Step 8: Caching for Performance

To improve performance, the result is cached at multiple levels (browser, OS, resolver) based on the Time to Live (TTL) value defined in the DNS record.
This caching prevents repeated queries for the same domain within a short period.

4. Common DNS Record Types

5. Recursive vs. Iterative DNS Queries

• Recursive Query: The resolver does all the work for the client and returns the final answer (used by browsers and end-users).
• Iterative Query: Each DNS server returns the best information it has, and the client must query the next server (used internally between DNS servers).

6. DNS Caching and TTL

Caching reduces latency and bandwidth usage, but outdated caches can cause propagation delays.
Each DNS record includes a TTL (Time to Live), typically between 60 seconds and 48 hours. When the TTL expires, the resolver must perform a fresh lookup.

7. DNS over HTTPS (DoH) and DNS over TLS (DoT)

To enhance privacy and prevent DNS hijacking or eavesdropping, modern browsers and resolvers use encrypted DNS protocols:

• DNS over HTTPS (DoH): Encrypts DNS queries using HTTPS.
• DNS over TLS (DoT): Encrypts DNS queries at the transport layer using TLS.

Examples:

• Cloudflare DoH: https://1.1.1.1/dns-query
• Google DoH: https://dns.google/dns-query

8. Common DNS Issues and Troubleshooting

• DNS Propagation Delay: Changes to DNS records may take hours to update worldwide due to caching.
• DNS Spoofing / Cache Poisoning: Attackers insert false DNS records to redirect users to malicious sites.
• Timeouts: Misconfigured DNS servers or blocked ports (UDP/TCP 53) can cause resolution failures.

Useful command-line tools:

nslookup example.com
dig example.com
ping example.com
traceroute example.com

9. Summary

The DNS system is the silent backbone of the Internet — translating human-friendly domain names into machine-readable IP addresses, enabling seamless web browsing, email delivery, and cloud service communication.

From root servers to authoritative servers, each component plays a critical role in ensuring that when you type a URL, your browser knows exactly where to go — all within milliseconds.

10. Key Takeaways

• DNS acts as the Internet’s distributed directory service.
• The resolution process involves recursive queries through multiple DNS layers.
• Caching and TTL improve speed but can delay DNS updates.
• Modern protocols like DoH and DoT add security and privacy.
• Proper DNS configuration is vital for web availability and performance.

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