Skip to content
finote

16. DNS

Introduction

Section titled “Introduction”

DNS (Domain Name System) is the phonebook of the internet. It translates human-readable domain names (like example.com) into IP addresses (like 192.0.2.1) that computers use to communicate. Without DNS, you would need to remember numeric IP addresses for every website you visit. Understanding DNS helps you comprehend how web requests work and how browsers find websites.

What is DNS?

Section titled “What is DNS?”

DNS is a hierarchical, distributed naming system that:

  • Maps domain names to IP addresses: Translates names to numbers
  • Distributes responsibility: Multiple servers handle different parts
  • Caches responses: Stores lookups for faster access
  • Provides redundancy: Multiple servers for reliability

How DNS Works

Section titled “How DNS Works”

The Lookup Process

Section titled “The Lookup Process”

When you type a URL in your browser:

  1. Browser checks cache: Looks for recent DNS lookup
  2. OS checks cache: Checks system DNS cache
  3. Resolver query: Queries DNS resolver (usually ISP)
  4. Root server: Queries root DNS servers
  5. TLD server: Queries top-level domain server (.com, .org)
  6. Authoritative server: Queries domain’s nameserver
  7. Response: Returns IP address
  8. Caching: Stores result for future use

DNS Resolution Steps

Section titled “DNS Resolution Steps”

DNS Record Types

Section titled “DNS Record Types”

A Record

Section titled “A Record”

Maps domain to IPv4 address:

example.com → 192.0.2.1

AAAA Record

Section titled “AAAA Record”

Maps domain to IPv6 address:

example.com → 2001:db8::1

CNAME Record

Section titled “CNAME Record”

Alias for another domain:

www.example.com → example.com

MX Record

Section titled “MX Record”

Mail exchange server:

example.com → mail.example.com

TXT Record

Section titled “TXT Record”

Text information (often for verification):

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

DNS Hierarchy

Section titled “DNS Hierarchy”

Domain Structure

Section titled “Domain Structure”
example.com
│      │
│      └─ Top-Level Domain (TLD)
└─ Second-Level Domain


subdomain.example.com
│        │      │
│        │      └─ TLD
│        └─ Domain
└─ Subdomain

Root Servers

Section titled “Root Servers”
  • 13 root servers: Worldwide distribution
  • Top-level: Handle .com, .org, .net, etc.
  • Distributed: Multiple locations for redundancy

DNS Caching

Section titled “DNS Caching”

Purpose

Section titled “Purpose”

Caching improves performance:

  • Faster lookups: Avoids repeated queries
  • Reduced load: Less traffic on DNS servers
  • Better performance: Faster page loads

Cache Levels

Section titled “Cache Levels”
  • Browser cache: Short-term storage
  • OS cache: System-level caching
  • Resolver cache: ISP/DNS provider cache
  • TTL: Time-to-live determines cache duration

Common DNS Issues

Section titled “Common DNS Issues”

DNS Propagation

Section titled “DNS Propagation”

Changes take time to propagate:

  • TTL settings: Control propagation speed
  • Global distribution: Servers worldwide
  • Caching: Existing caches delay updates

DNS Not Found

Section titled “DNS Not Found”

Common causes:

  • Incorrect domain: Typo in domain name
  • Not configured: DNS records not set up
  • Propagation delay: Changes not yet propagated

DNS in Web Development

Section titled “DNS in Web Development”

Domain Configuration

Section titled “Domain Configuration”

Setting up domains:

  • A records: Point to server IP
  • CNAME: Alias configurations
  • Subdomains: Create subdomains

CDN Integration

Section titled “CDN Integration”

CDNs use DNS for routing:

  • Geographic distribution: Route to nearest server
  • Load balancing: Distribute traffic
  • Performance: Faster content delivery

Best Practices

Section titled “Best Practices”

DNS Configuration

Section titled “DNS Configuration”
  • Use appropriate TTL: Balance between performance and flexibility
  • Set up redundant DNS: Multiple nameservers
  • Monitor DNS: Track DNS performance
  • Use DNS providers: Reliable DNS services

Performance

Section titled “Performance”
  • Minimize DNS lookups: Reduce number of domains
  • Use DNS prefetching: Pre-resolve domains
  • Monitor DNS latency: Track resolution times

References

Section titled “References”