Day 05 at rtCamp

Domain Name System (DNS)

DNS resolves human-readable domain names into IP addresses. For example, www.google.com → 142.250.182.100.

Process:

1. Browser checks cache
2. Queries OS resolver
3. Resolver checks root → TLD → Authoritative server
4. IP returned and cached

HTTP / HTTPS

• HTTP (Hypertext Transfer Protocol): Application-level protocol used for communication between clients and servers.
• HTTPS: Secured version of HTTP using SSL/TLS encryption.

Important Headers:

• Content-Type
• Authorization
• User-Agent
• Cache-Control

Curl example:
curl -I https://example.com

Status Codes:

• 200: OK
• 301/302: Redirect
• 403: Forbidden
• 404: Not Found
• 500: Server Error

How the Web Works

Client-Server Architecture

• Client (Browser) sends HTTP request
• Web server handles the request
• Server responds with HTML/CSS/JS
• Browser renders the content

Process:

1. DNS resolution
2. TCP connection (3-way handshake)
3. TLS handshake (for HTTPS)
4. HTTP request/response cycle
5. DOM construction and rendering

Emails: Protocols and Structure

Email System Involves:

• MUA: Mail User Agent (e.g., Outlook, Thunderbird)
• MTA: Mail Transfer Agent (e.g., Postfix, Exim)
• MDA: Mail Delivery Agent (e.g., Dovecot)

Protocols:

• SMTP: Sending emails
• POP3/IMAP: Retrieving emails

Sample PHP email (using mailpit or SMTP):

mail('to@example.com', 'Subject', 'Hello World', 'From: from@example.com');

SMTP, IMAP and POP: Email Protocols

Email communication relies on different protocol to send and receive emails from one client to the other. Those protocols are as follows:

• SMTP (Simple Mail Transfer Protocol): This protocol is used to send emails between servers and clients.
• IMAP (Internet Message Access Protocol): Allows email access to the email client while keeping message on the server.
• POP (Post Office Protocol): Downloads emails to a client and removed them from the server.

Protocol	Purpose	Storage
SMTP	Sending emails	N/A
IMAP	Receiving emails and syncing emails	Emails remain on the server
POP	Receiving emails	Emails are removed from the server

IMAP is preferred for accessing emails from multiple devices, whereas POP is useful for offline email access or where just a single devise is setup to receive email.