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DNS and Domain Names - Complete Guide

Understand how DNS translates domain names to IP addresses and how the domain name system works.

beginner📖 20 min read👁 6 views
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What You'll Learn

  • ✓ Master All Technologies concepts
  • ✓ Practical code examples
  • ✓ Real-world applications
  • ✓ Best practices & tips
💡 Pro Tip:

Bookmark this page and practice the examples in your own editor!

DNS and Domain Names - Complete Guide

What is DNS?

DNS (Domain Name System) is like the phonebook of the internet. It translates human-friendly domain names into computer-friendly IP addresses.

🌍 Why Do We Need DNS?

Without DNS:

You would have to remember: 142.250.190.46 to visit Google

With DNS:

You just type: google.com

DNS makes the internet user-friendly!

📝 What is a Domain Name?

A domain name is the address you type in your browser to visit a website.

Anatomy of a Domain Name:

https://www.example.com
  |     |    |      |
  |     |    |      └─ TLD (Top-Level Domain)
  |     |    └──────── Domain Name
  |     └───────────── Subdomain
  └─────────────────── Protocol

Examples:

  • google.com - Domain
  • www.google.com - Subdomain + Domain
  • mail.google.com - Different subdomain
  • api.github.com - API subdomain

🏗️ Domain Name Structure

1. Top-Level Domains (TLD)

Generic TLDs (gTLD):

  • .com - Commercial (most popular)
  • .org - Organization
  • .net - Network
  • .edu - Education
  • .gov - Government
  • .io - Tech startups
  • .dev - Developers

Country Code TLDs (ccTLD):

  • .us - United States
  • .uk - United Kingdom
  • .in - India
  • .jp - Japan
  • .de - Germany

2. Second-Level Domain (SLD)

The part you actually register:

  • In google.com, "google" is the SLD
  • In github.io, "github" is the SLD

3. Subdomain

Optional prefix to organize your site:

  • www.example.com (web server)
  • blog.example.com (blog)
  • shop.example.com (e-commerce)
  • api.example.com (API server)

🔄 How DNS Works

Step-by-Step DNS Lookup:

1. You Type a URL Browser: "I need to find example.com"

2. Check Browser Cache Browser: "Have I visited this recently?"

  • If YES: Use cached IP
  • If NO: Continue to step 3

3. Check OS Cache Operating System: "Do I have this cached?"

  • If YES: Return IP
  • If NO: Continue to step 4

4. Query DNS Resolver Your ISP: "Let me find this for you"

5. Query Root Server Root Server: "Try the .com nameserver"

6. Query TLD Server TLD Server: "Try example.com nameserver"

7. Query Authoritative Server Authoritative Server: "Here is the IP: 93.184.216.34"

8. Return to Browser Browser: "Got it! Connecting to 93.184.216.34"

🎯 DNS Record Types

A Record (Address)

Maps domain to IPv4 address

example.com → 93.184.216.34

AAAA Record

Maps domain to IPv6 address

example.com → 2606:2800:220:1:248:1893:25c8:1946

CNAME Record (Canonical Name)

Maps domain to another domain

www.example.com → example.com
blog.example.com → example.com

MX Record (Mail Exchange)

Directs email to mail servers

example.com → mail.example.com (Priority: 10)

TXT Record

Stores text information (often for verification)

example.com → "v=spf1 include:_spf.google.com ~all"

NS Record (Name Server)

Specifies authoritative name servers

example.com → ns1.example.com
example.com → ns2.example.com

⚡ DNS Caching

Why Caching?

DNS lookups take time. Caching speeds things up!

Cache Levels:

1. Browser Cache

  • Duration: Minutes to hours
  • Fastest lookup

2. Operating System Cache

  • Duration: Hours
  • Managed by OS

3. Router Cache

  • Duration: Hours to days
  • Shared by all devices

4. ISP Cache

  • Duration: Days
  • Serves many users

TTL (Time To Live)

TTL tells caches how long to store a record:

example.com  3600  IN  A  93.184.216.34
             |
             └─ TTL: 3600 seconds (1 hour)

🔍 DNS Lookup in Action

Using Command Line:

Windows:

nslookup google.com

Mac/Linux:

dig google.com

Using JavaScript:

// DNS lookup happens automatically
fetch("https://api.github.com")
  .then(response => response.json())
  .then(data => console.log(data));

// But you can see the resolved IP in browser DevTools

🛡️ DNS Security

DNS Spoofing / Cache Poisoning

Problem: Attacker tricks DNS to return wrong IP

Example:

  • You type: bank.com
  • Attacker makes DNS return: 123.45.67.89 (fake site)
  • You think you are on bank.com, but you are not!

Solution: DNSSEC (DNS Security Extensions)

DNSSEC

Adds cryptographic signatures to DNS records:

  • Verifies DNS responses
  • Prevents tampering
  • Ensures authenticity

🌐 Public DNS Servers

Instead of using your ISP DNS, you can use public DNS:

Google Public DNS

  • Primary: 8.8.8.8
  • Secondary: 8.8.4.4

Cloudflare DNS

  • Primary: 1.1.1.1
  • Secondary: 1.0.0.1
  • Focus on privacy and speed

OpenDNS

  • Primary: 208.67.222.222
  • Secondary: 208.67.220.220
  • Family-friendly filtering

Benefits:

  • Often faster
  • More reliable
  • Better privacy
  • Additional features (filtering, logging)

💻 Practical Examples

1. Check Your DNS Server

Windows:

ipconfig /all

Mac/Linux:

cat /etc/resolv.conf

2. Flush DNS Cache

Windows:

ipconfig /flushdns

Mac:

sudo dscacheutil -flushcache

Linux:

sudo systemd-resolve --flush-caches

3. View DNS Records

Using nslookup:

nslookup -type=A google.com
nslookup -type=MX google.com
nslookup -type=NS google.com

Using dig:

dig google.com A
dig google.com MX
dig google.com ANY

🎓 Real-World Scenario

Setting Up a Website:

1. Register Domain

  • Choose domain name
  • Register with registrar (GoDaddy, Namecheap, etc.)
  • Pay annual fee

2. Point to Hosting

  • Get hosting server IP: 123.45.67.89
  • Update A record: yourdomain.com → 123.45.67.89

3. Add Subdomain

  • Create CNAME: www.yourdomain.com → yourdomain.com
  • Create CNAME: blog.yourdomain.com → yourdomain.com

4. Set Up Email

  • Add MX records for email service
  • Add TXT records for verification

5. Wait for Propagation

  • DNS changes take 24-48 hours to spread globally
  • TTL affects propagation speed

📊 DNS Performance

Factors Affecting DNS Speed:

  1. Geographic Distance

    • Closer servers = faster response

  2. DNS Server Load

    • Busy servers = slower response

  3. Cache Status

    • Cached = instant
    • Not cached = lookup required

  4. Network Congestion

    • Busy network = delays

Measuring DNS Speed:

# Time a DNS lookup
time nslookup google.com

# Or use online tools
# - DNS Speed Test
# - DNSPerf.com

🔑 Key Takeaways

  1. DNS translates domain names to IP addresses
  2. Domain structure: subdomain.domain.tld
  3. DNS lookup involves multiple servers
  4. Caching speeds up subsequent lookups
  5. Different record types serve different purposes
  6. Security is important (use DNSSEC)
  7. Public DNS can be faster than ISP DNS

📚 Next Steps

  • Register your own domain name
  • Set up custom DNS records
  • Try different public DNS servers
  • Learn about DNS management tools
  • Explore advanced topics like load balancing with DNS

🔨 Practice Exercise

Check DNS records for your favorite websites:

# Check multiple record types
nslookup google.com
nslookup -type=MX google.com
nslookup -type=NS google.com

# Time the lookup
time nslookup github.com

# Compare different DNS servers
nslookup google.com 8.8.8.8
nslookup google.com 1.1.1.1

Now you understand how domain names work and how DNS powers the internet!