DNS

🌐 What is DNS? (Domain Name System)

DNS (Domain Name System) is like the internet’s phonebook.

It translates human-readable domain names (like google.com) into machine-readable IP addresses (like 142.250.192.46), so browsers can load websites.

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🔁 Why DNS Exists

Humans remember names, computers use IP addresses.
DNS maps names to IPs so you don’t have to type http://142.250.192.46 every time.

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⚙️ How DNS Works (Step-by-step)

When you type example.com in your browser:

1. Browser Cache Check
   First, it checks if it already knows the IP (cached).
2. OS Cache Check
   Your computer checks if it has the DNS result stored locally.
3. DNS Resolver (ISP)
   If not cached, it asks your configured DNS server (usually from your ISP).
4. Recursive Lookup Starts
   Resolver queries DNS hierarchy:
   • Root Server → Tells where .com servers are.
   • TLD Server (.com) → Tells where example.com’s nameserver is.
   • Authoritative Nameserver → Tells actual IP of example.com.
5. Response Back
   IP address is sent back through the resolver to your browser.
6. Browser Connects to IP
   Now it can connect and load the website.

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🗂️ DNS Hierarchy

. (root)
 └── .com (TLD)
     └── example.com (domain)
         └── www.example.com (subdomain)

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📄 Types of DNS Records

Record Type	Purpose	Example
A	Maps domain to IPv4 address	example.com → 93.184.216.34
AAAA	Maps domain to IPv6 address
CNAME	Alias to another domain	www.example.com → example.com
MX	Mail server info	For emails
TXT	Text data (e.g., SPF, verification)	SEO, domain ownership
NS	Points to name servers	Who handles your domain

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🔐 Advanced: DNS + Security

• DNSSEC: Protects against spoofing by signing DNS data.
• DNS over HTTPS (DoH) or DNS over TLS (DoT): Encrypts DNS traffic for privacy.