Skip to main content

Networking Basics

Table of Contents​

TCP/IP​

TCP/IP is how computers talk to each other on the internet.

What is IP?​

IP = Internet Protocol

  • Like the address system for the internet
  • Sends data packets from one computer to another
  • Doesn't check if packets arrive in order or if any are missing

What is TCP?​

TCP = Transmission Control Protocol

  • Works with IP to make sure data arrives correctly
  • Puts packets back in the right order
  • Asks for missing pieces to be sent again
  • Keeps connection between sender and receiver

Simple Comparison​

Think of sending a puzzle through mail:

  • IP = makes sure puzzle pieces get to the right address
  • TCP = puts the puzzle pieces together in correct order at the destination

How TCP Works (3-step handshake)​

  1. Sender says "Can we talk?" (SYN)
  2. Receiver says "Yes, let's talk" (SYN-ACK)
  3. Sender says "Great, here's my message" (ACK)

IP Versions​

  • IPv4 = older version, running out of addresses
  • IPv6 = newer version, has way more addresses available

Key Point​

  • IP sends the data
  • TCP makes sure it arrives correctly and in order
  • Together they make internet communication reliable

Deep Dive with TCP/IP Stack​

1. IP (Internet Protocol) - The Address System

IP Packet Structure (Like an envelope):

  • Version & IHL: Which IP version (IPv4 or IPv6) and header size
  • Source & Destination: Sender's address and receiver's address
  • TTL (Time-To-Live): Prevents packets from getting stuck in loops - decreases at each router
  • Checksum: Checks if header got damaged during travel

How Routing Works:

  • Routers read IP headers and find best path
  • Use routing protocols (OSPF, BGP) to make smart decisions
  • Real Example: When you access Netflix, routers find fastest path to their servers

2. TCP (Transmission Control Protocol) - The Reliable Delivery

Connection Setup (3-Way Handshake):

  • SYN: Client says "Want to connect?"
  • SYN-ACK: Server says "Yes, let's connect!"
  • ACK: Client says "Great, connection established!"

How TCP Makes Sure Data Arrives Correctly:

Sequencing:

  • Each packet gets a number (like pages in a book)
  • Receiver puts them back in correct order

Acknowledgments (ACKs):

  • Receiver says "Got packet #5"
  • If sender doesn't hear back, it resends the packet

Flow Control:

  • TCP adjusts speed based on receiver's capacity
  • Like adjusting water flow so the bucket doesn't overflow

Congestion Control:

  • Detects network traffic jams
  • Slows down sending when network is busy
  • Algorithms: TCP Reno, Cubic (smart traffic management)

Real Examples:

  • File Downloads: TCP ensures your movie download doesn't have missing parts
  • Web Browsing: Makes sure webpage loads completely and correctly
  • Video Streaming: For buffered content where quality matters more than speed

3. Operating System Implementation

Network Stack:

  • Lives in kernel (core part of OS)
  • Works on Linux, Windows, macOS

Socket API:

  • How programs talk to TCP/IP
  • Example: Java uses java.net.Socket to connect to internet

Performance Tricks:

Interrupt Coalescing:

  • Process multiple packets together
  • Reduces CPU workload (like handling mail in batches vs one letter at a time)

TCP Offloading:

  • Special network cards do TCP work instead of CPU
  • Makes data centers faster
  • Like having a dedicated mail sorter instead of doing it yourself

HTTP vs HTTPS​

What is HTTP?​

HTTP = Hypertext Transfer Protocol

  • It's the language browsers use to talk to websites
  • Two types of messages:
    • Requests = "Can I have this webpage?"
    • Responses = "Here's your webpage!"

HTTP is Not Secure​

Main Problem with HTTP:

  • HTTP sends everything in plain text (like sending a postcard)
  • Anyone watching can read your data easily
  • No protection for passwords, credit cards, or personal info

HTTP vs HTTPS - The Key Difference​

  • HTTP = Regular mail (anyone can read it)
  • HTTPS = Sealed envelope with lock (encrypted and secure)
  • HTTPS = HTTP + TLS/SSL encryption

The Security Problems with HTTP​

1. Everything is Readable:

  • When you type a password, it travels like this: password123
  • Hackers can easily see and steal it

2. No Identity Verification:

  • You can't be sure the website is real
  • Fake websites can pretend to be legitimate ones

How HTTPS Fixes This​

1. Encryption:

  • Your password becomes scrambled text like: t8Fw6T8UV81pQfyhDkhebbz7+oiwldr1j2gHBB3L3RFTRsQCpaSnSBZ78Vme+DpDVJPvZdZUZHpzbbcqmSW1+3xXGsERHg9YDmpYk0VVDiRvw1H5miNieJeJ/FNUjgH0BmVRWII6+T4MnDwmCMZUI/orxP3HGwYCSIvyzS3MpmmSe4iaWKCOHQ==
  • Hackers see gibberish instead of your real data

2. Authentication:

  • SSL certificates prove the website is real
  • Like showing an ID card to prove identity

How HTTPS Encryption Works​

  • Uses public key cryptography
  • Two keys: public (shared) and private (secret)
  • They create session keys for that specific conversation
  • All data gets scrambled with these keys

Attacks HTTPS Prevents​

  • On-path attacks = Someone intercepting your data
  • DNS hijacking = Redirecting you to fake websites
  • Domain spoofing = Fake websites pretending to be real ones

HTTP/HTTPS Deep Dive​

1. HTTP (HyperText Transfer Protocol) - The Web Language

Request/Response Model:

HTTP Methods (Like Different Types of Requests):

  • GET = "Give me this webpage" (just asking for info)
  • POST = "Here's some data to save" (sending form data)
  • PUT = "Update this information"
  • DELETE = "Remove this item"

Headers & Body:

  • Headers = Like envelope information (who sent it, what type of content, etc.)
  • Body = The actual message/content inside
  • Example: Content-Type tells if it's text, image, or video

Stateless Protocol:

  • Each request is independent (like amnesia - forgets previous conversations)
  • Cookies & Sessions = Ways to remember user info between requests
  • Like giving someone a ticket stub to remember they paid

HTTP Versions:

HTTP/1.1 (Older):

  • One request at a time per connection
  • Like having one phone line - wait for first call to finish

HTTP/2 (Newer & Faster):

  • Multiplexing = Multiple requests at same time on one connection
  • Like having multiple conversations on one phone line
  • Binary framing = More efficient data packaging
  • Header compression = Smaller, faster data transfer

Real Examples:

  • Web Browsing: Your browser uses HTTP to get webpages, images, videos
  • APIs: Apps use HTTP to get data from servers (like weather apps getting weather data)

2. HTTPS (HTTP Secure) - The Protected Version

SSL/TLS Layer (The Security Guard):

Encryption Process:

  • Scrambles data so only intended receiver can read it
  • Like speaking in secret code

Handshake Process (The Security Setup):

  • Client says: "Hi, I want secure connection" (ClientHello)
  • Server says: "Here's my ID card and security options" (ServerHello + Certificate)
  • Both agree: "Let's use these secret keys for our conversation"

Certificate Validation:

  • Client checks if server's ID card (certificate) is real
  • Like checking if someone's driver's license is legitimate
  • Certificate Authorities (CAs) = Trusted organizations that verify identities

Real Examples:

  • Online Shopping: Credit card info protected during purchase
  • Banking: Account details and transactions secured
  • Social Media: Login credentials and personal data protected

Real-World Use Cases​

Online Banking System:

What's Used:

  • TCP/IP: Makes sure money transfer data arrives correctly
  • HTTPS: Protects your login and transaction details

How It Works:

  • TCP/IP: If any data packet gets lost, it asks for it again (no missing money!)
  • HTTPS: Encrypts your password and account numbers
  • Result: Safe banking where hackers can't steal your info

Video Streaming (Netflix, YouTube):

What's Used:

  • TCP/IP: Delivers video chunks in correct order
  • HTTP/2: Downloads multiple video pieces at same time
  • HTTPS: Protects your viewing data and prevents piracy

How It Works:

  • TCP/IP: Video broken into small pieces, delivered in right order
  • HTTP/2: Multiple video segments download simultaneously = faster loading
  • HTTPS: Your viewing history and personal data stay private

Real-Time Chat Apps (WhatsApp, Discord):

What's Used:

  • TCP/IP: Makes sure messages arrive in correct order
  • WebSockets: Keeps connection open for instant messaging
  • HTTPS: Protects initial connection setup

How It Works:

  • TCP/IP: Messages delivered without loss or wrong order
  • WebSockets: After initial handshake, maintains open line for real-time chat
  • HTTPS: Login and sensitive data encrypted during setup

Key Differences Summary​

HTTP:

  • Fast but not secure
  • Like sending postcards (anyone can read)
  • Good for public information

HTTPS:

  • Slightly slower but very secure
  • Like sending sealed, encrypted letters
  • Essential for private/sensitive information

Performance Tips​

  • HTTP/2 makes websites much faster
  • Multiplexing = Multiple requests simultaneously
  • Compression = Smaller data transfers

Security Rule: Always use HTTPS for anything involving passwords, personal info, or payments!

Load Balancers​

What is a Load Balancer?​

Main Idea:

  • A load balancer is like a traffic director for websites
  • It spreads incoming requests across multiple servers
  • Prevents any single server from getting overwhelmed

Benefits: Availability, Security, Scalability, Performance

Load Balancing Algorithms (How it Decides)​

Static Methods:

  • Round Robin = Takes turns (Server 1, Server 2, Server 3, repeat)
  • Threshold = Based on set limits

Dynamic Methods:

  • Least Connections = Sends to server with fewest active users
  • Least Time = Sends to fastest responding server
  • Random with Two Choices = Picks two servers randomly, then chooses the better one

Smart Methods:

  • URL Hash = Same webpage always goes to same server
  • Source IP Hash = Same user always goes to same server
  • Consistent Hashing = Advanced method for large systems

Types of Load Balancers​

By Location in Network:

  • Layer 4 = Works with basic network info (IP addresses, ports)
  • Layer 7 = Works with website content (HTTP, cookies, URLs)

Special Types:

Application Load Balancing:

  • Focuses on specific apps and their needs

Global Server Load Balancing:

  • Sends users to nearest server worldwide
  • Like having local stores in different cities

DNS Load Balancing:

  • Uses domain name system to distribute traffic

Internal Load Balancing:

  • Works inside company networks (not public internet)

CDN (Content Delivery Network)​

What is a CDN?​

CDN = Content Delivery Network

  • A group of servers spread around the world
  • They store copies of website content (images, videos, webpages)
  • Send content to users from the closest server

1. Performance (Speed) 🚀​

How CDNs Make Websites Faster:

  • Shorter Distance = Content comes from nearby server instead of far away
  • Smaller Files = CDN compresses files to load faster
  • Better Servers = Optimized to respond quickly

Real Results:

  • Websites see 50% faster load times or more
  • Pages that took 4 seconds now load in 2 seconds

2. Reliability (Always Working) 🛡️​

How CDNs Keep Websites Online:

  • Load Balancing = Spreads traffic so no single server gets overwhelmed
  • Failover = If one server breaks, backup server takes over automatically
  • Route Around Problems = Like GPS finding alternate routes during traffic jams
  • Multiple Backups = Many servers in different locations

Simple Example: If the server in New York goes down, users automatically get content from the server in Chicago

3. Cost Savings 💰​

How CDNs Save Money:

  • Less Data Transfer = Origin server doesn't have to send same content repeatedly
  • Bandwidth Costs = Web hosts charge for data transfer - CDN reduces this
  • CDN Handles Most Requests = Origin server does less work

Simple Example: Instead of your main server sending a popular image 1000 times, CDN sends it 999 times and your server only sends it once

4. Security (Attack Protection) 🔒​

How CDNs Protect Websites:

  • DDoS Protection = Can absorb massive attack traffic
  • Multiple Servers = Harder to overwhelm than single server
  • Traffic Distribution = Spreads attack across many servers
  • Keeps Sites Online = Even during attacks

Simple Example: If hackers send 1 million fake requests, CDN's many servers can handle it better than one server trying to handle everything

How CDNs Work​

Caching Process:

  1. User requests a webpage
  2. CDN checks if it has a copy stored nearby
  3. If yes, sends it immediately (fast!)
  4. If no, gets it from main server and saves a copy for next time

Geographic Distribution:

  • Servers in many countries and cities
  • Users get content from closest location
  • Reduces travel time for data

Real-World Impact​

Before CDN:

  • Slow loading websites
  • Sites crash during high traffic
  • Expensive bandwidth costs
  • Vulnerable to attacks

After CDN:

  • Fast loading from anywhere in the world
  • Stays online during traffic spikes
  • Lower hosting costs
  • Protected from most attacks