🌐 DNS Learning Center

Master the Domain Name System with interactive lessons and hands-on practice

Overview
How DNS Works
Record Types
DNS Header
DNS Builder
Quiz

What is DNS?

The Domain Name System (DNS) is like the phone book of the internet. It translates human-readable domain names (like google.com) into IP addresses (like 172.217.12.142) that computers use to communicate.

Why Do We Need DNS?

  • User-Friendly: Remembering "google.com" is easier than "172.217.12.142"
  • Flexibility: Websites can change IP addresses without users noticing
  • Load Distribution: One domain can point to multiple servers
  • Hierarchical Structure: Distributes the workload across millions of servers

Key Components

🏠 Resolver

Your device's DNS client

→

🏢 Recursive Server

ISP's DNS server

→

🌍 Root Servers

Top-level directory

→

📋 Authoritative

Final answer source

How DNS Resolution Works

When you type a website address, here's what happens behind the scenes:

1. Query Starts

You type "example.com" in your browser

→

2. Check Cache

System checks local DNS cache

→

3. Recursive Query

Ask ISP's DNS server

→

4. Root Server

Ask "Where are .com servers?"

→

5. TLD Server

Ask "Where is example.com?"

→

6. Authoritative

Get the final IP address

→

7. Connection

Browser connects to website

DNS Hierarchy

DNS uses a tree-like structure:

  • Root (.) - The top of the hierarchy
  • Top-Level Domains (TLD) - .com, .org, .net, country codes
  • Second-Level Domains - google, facebook, example
  • Subdomains - www, mail, ftp

DNS Record Types

DNS stores different types of information using various record types:

A Record

Domain → IPv4 Address

AAAA Record

Domain → IPv6 Address

CNAME Record

Domain Alias

MX Record

Mail Server

NS Record

Name Server

TXT Record

Text Data

PTR Record

Reverse Lookup

DNS Header Format

Every DNS message contains a 12-byte header with the following structure:

DNS Header (12 bytes)

0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
ID (16 bits)
QR
Opcode
AA
TC
RD
RA
Z
RCODE
QDCOUNT (16 bits)
ANCOUNT (16 bits)
NSCOUNT (16 bits)
ARCOUNT (16 bits)

Field Descriptions

  • ID: Unique identifier for matching queries with responses
  • QR: Query (0) or Response (1)
  • Opcode: Type of query (Standard, Inverse, Status)
  • AA: Authoritative Answer flag
  • TC: Truncation flag (message was truncated)
  • RD: Recursion Desired flag
  • RA: Recursion Available flag
  • Z: Reserved for future use (must be zero)
  • RCODE: Response code (No Error, Format Error, Server Failure, etc.)
  • QDCOUNT: Number of questions
  • ANCOUNT: Number of answer records
  • NSCOUNT: Number of authority records
  • ARCOUNT: Number of additional records

DNS Record Builder

Create your own DNS records and see how they work!

Build a DNS Record

Click "Create DNS Record" to see your DNS records here!

DNS Lookup Simulator

Enter a domain and click "Simulate DNS Lookup" to see the resolution process!

DNS Knowledge Quiz

Test your understanding of DNS concepts!