✅ Define the Domain Name System (DNS) and explain its function.
What is an IP Address? 📍
Internet Protocol (IP) Address: A unique numerical label assigned to each device connected to a computer network that uses the Internet Protocol for communication.
Think of it as a digital street address for your computer, phone, or any other connected device.
It ensures data packets are routed to the correct destination across the internet.
🏠 Metaphor: Address vs. IP — Side by Side
Click each card to explore the analogy:
🏠
Physical Address
Thamel, Kathmandu 44600
💻
IPv4 Address
192.168.1.1
🌐
IPv6 Address
2001:0db8::1
Select a card above to see the breakdown.
The Two Flavors of IP: IPv4 vs. IPv6
IPv4 (The Original)
Example: 192.168.1.1
The first widely used version.
32-bit address space.
Supports ~4.3 billion unique addresses.
We've nearly run out! 📉
IPv6 (The Future)
Example: 2001:0db8:85a3::8a2e:0370:7334
The new standard.
128-bit address space.
Supports a virtually limitless number of addresses.
Solves the address exhaustion problem. 📈
📊 Visualize: IPv4 vs IPv6 Address Space
IPv4
~4.3 billion addresses
IPv6
3.4 × 10³⁸ addresses
Press "Fill Tanks" to see how full each address space is.
🔢 Interactive: IPv4 Address Decoder
11000000
.
10101000
.
00000001
.
00000001
192.168.1.1
32 bits total
11000000.10101000.00000001.00000001
The Problem with Numbers
Computers are great at remembering numbers like:
142.250.190.78
Humans? Not so much.
Which is easier to remember?
142.250.190.78 or google.com?
Challenge: How do we bridge the gap between human-friendly names and computer-friendly numbers?
🧠 Challenge: Can You Remember IPs?
Round 1 of 2 — Memorize the IP address:
Ready
vs.
The Internet's Phonebook: DNS 📖
Domain Name System (DNS): A global, decentralized system that translates human-readable domain names (like www.google.com) into the numerical IP addresses that computers use to communicate.
Without DNS, we'd have to memorize IP addresses for every website we want to visit.
It's a critical, yet often invisible, service that makes the web user-friendly.
📖 Transform: Phonebook → DNS
📖
Phonebook
Arjun Sharma
Human name
→
📞
Phone Number
9841-XXXXXX
Numeric identifier
A phonebook maps a person's name to their phone number. DNS works the same way for the internet — but at global scale.
How DNS Works: A 4-Step Journey 🔍
1. Request: You type www.google.com into your browser and hit Enter.
2. Query: Your computer sends a request to a DNS server, asking "What is the IP address for www.google.com?"
3. Lookup & Respond: The DNS server looks up the domain in its database, finds the corresponding IP address (e.g., 142.250.190.78), and sends it back to your computer.
4. Connect: Your browser now uses that IP address to connect directly to Google's web server.
⚡ This entire process happens in milliseconds! ⚡
🌐 Animation: DNS Lookup in Action
💻
Your Browser
→
🏠
ISP DNS Resolver
→
🌍
Root Server
→
🔤
.com TLD Server
→
📋
Auth. Nameserver
←
🌐
Web Server
Ready
Press Next Step to begin.
Step 0 of 6
✅ DNS resolved! Browser now connects directly to 43.229.84.12 — your ISP caches this for faster access next time.
Practical Application: DNS in Nepal 🇳🇵
When you visit a local Nepali website, the DNS process is essential for a fast connection.
Example: Visiting a local news site
You type www.ekantipur.com.
Your Internet Service Provider (e.g., WorldLink, NTC) has its own DNS server. It quickly resolves this local domain name to an IP address, often for a server located within Nepal.
This local resolution reduces latency, making Nepali websites load faster for users inside the country.
⚡ Race: Nepal DNS vs. International DNS
Resolving www.ekantipur.com — Click Race to compare:
NTC/WorldLink DNS (ISP, in Nepal)
8.8.8.8 (Google DNS) (International)
1.1.1.1 (Cloudflare) (International)
ISP DNS servers are physically closer to you in Nepal, so they resolve local domains faster. International DNS must route through undersea cables.
What if DNS Suddenly Stopped? 🤯
Discussion Question: What would happen to the internet if the global DNS system went offline?
Human-friendly domain names (google.com, facebook.com) would stop working.
Email routing, which relies on domain names, would fail.
The internet would still technically function, but you would need to know the exact IP address of every server you wanted to connect to.
In short, the web as we know it would become almost unusable for most people.
🆘 Challenge: Navigate Without DNS
DNS is offline. You must type the exact IP address to visit any site.
Enter IP address to navigate...
Select a site you want to visit, then enter its IP address.
Go to:
Attempts: 0 | Correct: 0
Summary & Key Takeaways 🎯
An IP address is a unique numerical label for a device on the internet, acting like a digital street address.
DNS is the internet's phonebook, translating easy-to-remember domain names into the IP addresses computers need.
IPv6 was created to solve the problem of running out of the ~4.3 billion available IPv4 addresses, ensuring the internet can continue to grow.
Understanding Client-Server Architecture
Next focus
In this part of today's lecture, you will be able to:
✅ Define client-server architecture.
✅ Describe the role of a client.
✅ Describe the role of a server.
✅ Explain the request-response model.
The Foundation of the Modern Internet
Client-Server Architecture: A computing model where a central server hosts, delivers, and manages resources and services for one or more clients.
Think of it as a restaurant: you (the client) order from the kitchen (the server).
The Two Key Players 📊
The Client
Requests services.
Interacts directly with the end-user.
Examples: Web Browser, Mobile App, Email Client (Outlook)
The Server
Provides services.
Waits for and responds to client requests.
Examples: Web Server, Database Server, Mail Server
🔍 Deep Dive: The Client
The client is any computer or program that requests services or resources from a server.
Example: Your Web Browser
When you type www.google.com into Chrome, Firefox, or Safari...
...your browser acts as the client, sending a request for the Google homepage.
⚡ Deep Dive: The Server
The server is a powerful computer or program dedicated to providing services to clients.
Web Server
Stores website files (HTML, CSS, images) and "serves" them to browsers upon request.
Mail Server
Manages the sending, receiving, and storing of emails for clients like Gmail or Outlook.
Servers are designed to handle many requests at once and run 24/7.
The Request-Response Model
This is the core communication cycle of the client-server architecture.
1. Request: The Client sends a request to the Server. (e.g., "Get me the homepage for ekantipur.com")
2. Process: The Server receives the request, finds the necessary resources, and processes it. (e.g., Locates the HTML file for the homepage)
3. Response: The Server sends a response back to the Client. (e.g., The HTML, CSS, and image files for the page)
Visualizing the Cycle
1. Client Request
💻➡️🌐
Your browser asks for a website.
2. Server Processes
⚙️🗄️
The web server finds the requested files.
3. Server Response
💻⬅️🌐
The server sends the website data back.
This entire cycle often happens in milliseconds!
Practical Application in Nepal
Using eSewa or Khalti
Client: Your smartphone app (the eSewa/Khalti app).
Request: You tap "Pay" for your NTC mobile top-up.
Server: The eSewa/Khalti server receives the request, validates your account, securely communicates with the NTC server, and processes the payment.
Response: The server sends a "Transaction Successful" message back to your app.
Key Takeaways
Client-server is the fundamental architecture of the internet.
The client is the requester (e.g., your browser).
The server is the provider (e.g., a web server).
All communication happens through a simple but powerful request-response cycle.
Discussion Questions
When you use a mobile app like Instagram, which part is the client and which part is the server?
What are some of the advantages of the client-server model? (Think about centralization, security, and maintenance).
Can a computer be both a client and a server? Explain.
Thank You
Questions before we wrap this hour?
Next: Unit 6 · Session 3 — HTTP, Email, FTP, WWW, Search, and TELNET