DNS Fundamentals

Domain Name System Core Concepts

What is DNS?

Domain Name System (DNS) translates human-readable domain names into IP addresses that computers use to communicate.

DNS Resolution Process:

1. User enters domain name in browser
2. Browser checks local cache
3. Query sent to recursive resolver
4. Root nameserver queried
5. TLD nameserver queried
6. Authoritative nameserver returns IP

DNS Record Types

A Record

Maps domain to IPv4 address (192.0.2.1)

AAAA Record

Maps domain to IPv6 address

CNAME Record

Maps alias to canonical name

MX Record

Mail exchange server

Time To Live (TTL)

TTL determines how long DNS records are cached by resolvers and browsers.

Short TTL (60-300s): For records that change frequently
Medium TTL (1-24 hours): For most production records
Long TTL (24+ hours): For stable records
Lower before changes: Reduce propagation time

Route 53 Features

Key Benefits

100% uptime SLA
Global anycast network
Health checks and monitoring
Traffic routing policies

Integration

AWS services integration
Domain registration
Cost-effective pricing
Easy management via console/API

Exam Strategy Tip

Remember: A records map to IP addresses, CNAME cannot be used for root domain. TTL affects propagation time - lower TTL before making changes. Route 53 provides 100% uptime SLA.

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