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DNS

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🌐 DNS (Domain Name System)

DNS is the phonebook of the internet. Just like you use a phonebook to look up "Pizza Palace" and find their phone number, DNS looks up "www.google.comarrow-up-right" and finds its IP address.

It converts human-friendly domain names:

www.example.com
api.mycompany.io

into machine-friendly IP addresses:

93.184.216.34
203.0.113.10

DNS translates between these two, so you don't have to memorize numbers!

Why DNS Exists

Every device on the internet has an IP address - a unique numerical identifier like 172.217.14.238.

The problem: Imagine having to remember:

  • Google: 142.250.185.46

  • Facebook: 157.240.241.35

  • Amazon: 52.94.236.248

  • Netflix: 54.155.246.232

That's impossible! DNS solves this by letting you use memorable names instead.

Real-world analogy: Your contacts app stores "Mom" → 555-1234. You say "Call Mom" and your phone handles the number lookup. That's exactly what DNS does for websites!

Where DNS is Used

DNS is everywhere on the internet:

  • Web browsing - Every website you visit

  • Email - Finding mail servers (Gmail, Outlook)

  • Mobile apps - Apps connecting to their servers

  • Gaming - Finding game servers

  • Streaming - Connecting to Netflix, Spotify, YouTube

  • IoT devices - Smart home devices finding their services

Basically, every time you type a web address or an app connects to the internet, DNS is working behind the scenes!

How DNS Works: The Lookup Process

When you type www.example.com in your browser, here's what happens:

The DNS Hierarchy: Understanding Domain Names

Domain names are organized hierarchically, read from right to left:

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DNS Server Types

There are several types of DNS servers in the lookup chain:

1. DNS Resolver (Recursive Resolver)

  • Your ISP's or public DNS server (like Google's 8.8.8.8)

  • Does all the hard work for you

  • Caches results for speed

  • Analogy: A librarian who finds books for you

2. Root DNS Servers

  • 13 root server networks worldwide (labeled A through M)

  • Knows where to find TLD servers

  • Analogy: The library's main directory

3. TLD (Top-Level Domain) Servers

  • Handles specific extensions (.com, .org, .net, .uk, etc.)

  • Knows where to find authoritative servers

  • Analogy: The section catalog (Fiction, Non-Fiction, etc.)

4. Authoritative Name Servers

  • Holds the actual DNS records for a domain

  • The final authority on a domain's information

  • Analogy: The specific book with your answer

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DNS Record Types

DNS stores different types of information using various record types:

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DNS Caching: Why Websites Load Fast

DNS uses caching at multiple levels to speed things up:

TTL (Time To Live): Each DNS record has a TTL that says "cache me for X seconds." After that, the cache expires and a fresh lookup happens.

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Real-World Example: What Happens When You Visit Google

Let's walk through a complete example:

Next time you visit: Browser cache returns the IP in <1ms!

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DNS Protocol Details

DNS typically uses UDP on port 53. Remember UDP from earlier?

Why UDP?

  • DNS queries are small (usually one packet)

  • Speed is important

  • If no response, just retry

  • Perfect for simple question-answer exchanges

Example DNS Query/Response:

When DNS uses TCP:

  • Zone transfers (copying entire DNS databases between servers)

  • Responses larger than 512 bytes

  • As a fallback if UDP fails

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DNS Security: Problems and Solutions

Problems with Traditional DNS:

  1. No Encryption - Anyone can see what websites you visit

  2. DNS Spoofing - Attackers can fake DNS responses

  3. Cache Poisoning - Injecting fake records into caches

  4. Man-in-the-Middle - ISPs or attackers modifying responses

Modern Solutions:

DNSSEC (DNS Security Extensions)

  • Adds digital signatures to DNS records

  • Verifies authenticity

  • Prevents tampering

DNS over HTTPS (DoH)

  • Encrypts DNS queries using HTTPS

  • Hides your lookups from ISPs

  • Used by Firefox, Chrome, Edge

DNS over TLS (DoT)

  • Similar to DoH but uses TLS directly

  • Port 853 instead of 443

Public DNS Servers

You can choose which DNS resolver to use:

Provider
Primary DNS
Secondary DNS
Features

Google

8.8.8.8

8.8.4.4

Fast, reliable

Cloudflare

1.1.1.1

1.0.0.1

Privacy-focused, fast

OpenDNS

208.67.222.222

208.67.220.220

Filtering, security

Quad9

9.9.9.9

149.112.112.112

Malware blocking

Why change?

  • Faster lookups

  • Better privacy

  • Parental controls

  • Malware blocking

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Simple Practical Examples

Example 1: Checking DNS Records

You can look up DNS records using command-line tools:

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Example 2: DNS Propagation

When you change DNS records (like pointing your domain to a new server):

This is why website moves take time to fully complete.

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Example 3: Subdomains for Services

Companies use subdomains to organize services:

Each can point to a different IP address!

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How DNS Handles Millions of Queries

Load Distribution:

  • Multiple servers with same IP (anycast)

  • Geographically distributed

  • Closest server responds

Example: Google's 8.8.8.8 isn't one server - it's thousands worldwide! Your query goes to the nearest one.

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Summary and key points

DNS is essential because:

  • Translates human-friendly names to machine addresses

  • Makes the internet usable (no memorizing numbers!)

  • Works incredibly fast through caching

  • Operates at massive scale (billions of queries/day)

  • Uses a hierarchical, distributed system

Key Points:

  • DNS lookups happen for almost every internet action

  • Caching makes repeat visits instant

  • Usually uses UDP for speed

  • Organized hierarchically (Root → TLD → Domain → Subdomain)

  • Can be secured with DNSSEC, DoH, or DoT

Remember: Every time you:

  • Visit a website

  • Send an email

  • Use an app

  • Stream video

DNS is working silently in the background, translating names to numbers in milliseconds!

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