Telusko Docs

DNS stands for Domain Name System. It is the system responsible for translating human-readable domain names (like telusko.com) into machine-readable IP addresses (like 192.168.1.1) that computers use to communicate with each other.

DNS is often called the "phonebook of the internet."

Key Terminology

Term	Meaning
Domain	A specific URL or web address (e.g., `telusko.com`)
Subdomain	A domain created under a parent domain (e.g., `docs.telusko.com`, `courses.telusko.com`)
IP Address	A numerical identifier assigned to every device/server on the internet

Why Do We Need DNS?

There are more than 350 million domains registered on the internet. Storing all of them directly in the browser is impractical because:

Storage Limitation — Browsers would need massive storage to maintain a mapping of all domains to IP addresses, degrading performance.
Dynamic IP Changes — IP addresses for domains can change at any time, and updating every browser individually is not feasible.

DNS solves this by acting as a centralized lookup service that resolves domain names to their current IP addresses on demand.

How DNS Resolution Works

When you type a URL (e.g., telusko.com) into your browser, the following process occurs:

DNS_Flow

1. DNS Resolver (via ISP)

Your machine connects to the internet through an Internet Service Provider (ISP).
The ISP has a DNS Resolver — the component responsible for finding the correct IP address for any domain you request.

2. Root Server

The DNS Resolver first contacts a Root Server.
There are 13 root servers worldwide, named a.root-server.net through m.root-server.net.
These 13 servers are owned and operated by various organizations.
The root server does not know the final IP address — it directs the resolver to the appropriate TLD server.

3. TLD Server (Top-Level Domain)

TLD servers handle domains grouped by their extension.
Common TLDs:

TLD	Category
`.com`	Commercial
`.net`	Network
`.gov`	Government
`.edu`	Education
`.in`	India (country-specific)

The TLD server responds with the IP address of the Authoritative Name Server that manages the specific domain.

4. Authoritative Name Server

This server holds the actual DNS records for the domain.
It contains zones — each zone manages a specific domain and all its subdomains.
Returns the final IP address of the requested domain to the DNS Resolver.

5. Browser Receives the IP

The DNS Resolver returns the IP address to the browser.
The browser makes a direct call to that IP address and loads the webpage.

DNS Resolution

User types: telusko.com
        |
        v
   DNS Resolver (ISP)
        |
        v
   Root Server (a–m.root-server.net)
        |  Returns: IP of .com TLD server
        v
   TLD Server (.com)
        |  Returns: IP of Authoritative Name Server
        v
   Authoritative Name Server
        |  Returns: IP of telusko.com
        v
   Browser connects to IP → Webpage loads

DNS Caching

The entire DNS resolution process happens only once for a given domain. On subsequent visits, the IP address is fetched from cache.

Cache Levels (checked in order)

Level	Location	Description
1	Browser Cache	Browser stores recently resolved domains locally
2	OS Cache	Operating system maintains its own DNS cache
3	DNS Resolver Cache	The ISP's resolver caches results for all users

Caching significantly reduces latency and load on DNS infrastructure by avoiding repeated lookups for the same domain.

Benefits_of_Cache_Caching

Zones and Subdomains

An Authoritative Name Server can have multiple zones attached to it.
Each zone is dedicated to a specific domain.
A zone contains records for the main domain and all its subdomains.

Example — Zone for telusko.com:

telusko.com        →  93.184.216.34
docs.telusko.com   →  93.184.216.35
courses.telusko.com →  93.184.216.36

Key Takeways of DNS Components

Component	Role
DNS Resolver	Initiates the lookup process and returns the final IP to the browser
Root Server	First point of contact; directs to the correct TLD server (13 globally)
TLD Server	Manages top-level domains (.com, .net, etc.); points to authoritative server
Authoritative Name Server	Holds actual domain-to-IP mappings in zones
Cache	Stores resolved IPs at browser, OS, and resolver level to avoid repeat lookups

Summary

DNS translates domain names into IP addresses so browsers can locate servers on the internet.
The resolution follows a hierarchy: Root Server → TLD Server → Authoritative Name Server.
There are 13 root servers (A through M) managed by different organizations worldwide.
DNS results are cached at multiple levels (browser, OS, resolver) to improve performance.
Each authoritative server manages zones, where each zone holds a domain and all its subdomains.
This entire lookup happens only on the first visit — subsequent requests are served from cache.

Written By: Muskan Garg

What is DNS?