Lecture 1: Internet & Networking Basics

How Internet Works

Principles

1. Share Data -> Direct cable link -> bits(1/0).
2. Scaling Issue -> Use a switch -> Local
3. Connecting Networks -> Use Routers -> Internetwork.
4. Finding Devices -> IP Address(unique for each device).
5. Reliabilty -> Break data into Packets -> TCP/IP protocol.

IP Address

• IPv4: 32-bit (e.g., 172.217.16.142) → limit ~4.3B.
• IPv6: 128-bit (2^128 ≈ 340 undecillion addresses).
• Public IP → Unique, given by ISP, visible on internet.
• Private IP → Local use only (192.168.x.x, etc.).

MAC Address

• Hardware ID (burned into device).
• Format: 3C:22:FB:A3:B4:C5 (48-bit).
• Used within local network.

Port Numbers (0–65535)

• Well-known (0–1023): HTTP (80), HTTPS (443), SSH (22).
• Registered (1024–49151): MySQL (3306), MongoDB (27017), Node.js (3000).
• Dynamic/Ephemeral (49152–65535): Temporary, client-side.

DNS(Domain Name System)

• Converts domain → IP.
• Process:
  1. Check cache (browser/OS/router).
  2. Ask Recursive Resolver (ISP/Google 8.8.8.8).
  3. Resolver queries:
     • Root → TLD (.com) → Authoritative (google.com).
  4. Returns IP to browser.
• Browser connects to IP on correct port (e.g., 443).