DNS (Domain Name System) Basics
The DNS (Domain Name System) acts as the address book of the internet. Its role is to translate human-readable Domain Names (e.g., www.google.com) into computer-understandable IP Addresses (e.g., 172.217.161.164) that servers use for communication.
Without DNS, users would have to type complex IP addresses to access websites.
1. Working Principle: The Resolution Process
When a user enters a domain name, several steps are taken to obtain the corresponding IP address. This process is called Name Resolution.
- Query Resolver: The user's device (browser) sends a DNS query to a DNS Resolver. (Usually provided by the ISP or a public service like Google DNS).
- Root Server Query: The Resolver queries a Root Name Server to find the address of the server handling the Top-Level Domain (TLD, such as
.comor.org). - TLD Server Query: The Resolver then queries the TLD Name Server to get the address of the Authoritative Name Server that manages the specific domain (e.g.,
google.com). - Final IP Acquisition: The Resolver queries the Authoritative Name Server, which finally returns the IP Address for
www.google.comback to the user's device.
2. DNS Hierarchical Structure
DNS is structured as a hierarchical, distributed database in a pyramid shape.
| Level | Role | Example |
|---|---|---|
| Root Domain | The top level of the hierarchy, managed by 13 logical server groups worldwide. | . (dot) |
| Top-Level Domain (TLD) | Country codes (.kr, .jp) or generic domains (.com, .org, .net). |
.com |
| Second-Level Domain | The unique name purchased by the user. | google |
| Subdomain | Specific service areas within the website. | www, mail |
3. DNS Communication Protocol
DNS query communication primarily uses UDP (User Datagram Protocol).
- Reason: Since DNS queries are small, single request/response messages, fast response time (UDP) is much more efficient than the overhead of guaranteed reliability (TCP).