Theoretical Booklet – What’s in the Digital World?

📘 Cyber Rangers – Module 1, Session 2

Theoretical Booklet: What’s in the Digital World?
How the Internet Works, One Packet at a Time

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🌐 1. What Is a Network?

A network is a group of devices connected together so they can communicate and share data. These devices can include computers, smartphones, servers, printers, and other hardware.

Networks are built using:

• Cables (Ethernet)
• Wireless signals (Wi-Fi, Bluetooth)
• Switches (connect devices in a local network)
• Routers (connect one network to another)

Types of Networks:

Type	Meaning	Example
LAN	Local Area Network	School or home network
WAN	Wide Area Network	Telecom provider’s infrastructure
PAN	Personal Area Network	Bluetooth between a phone and earbuds
Internet	A global WAN	Billions of devices worldwide

💡 Tip: All internet activity starts inside a small LAN (your home or school) and then connects to the wider internet using a router.

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🌍 2. So What Is the Internet, Really?

The Internet is a global system of interconnected networks using the TCP/IP protocol. It’s a physical infrastructure made up of:

• Fiber optic cables (often under oceans)
• Data centers and servers
• Internet Exchange Points (IXPs)
• Routers and switches

The Internet does not have a single owner — it’s made up of thousands of independent networks that follow global standards.

Important Layers in Internet Communication:

1. Physical layer – The actual wires, cables, and radio waves
2. Data Link layer – Controls data transfer between devices
3. Network layer (IP) – Handles addressing and routing
4. Transport layer (TCP) – Ensures delivery is accurate and complete
5. Application layer – The services we use (web, email, games)

🧠 You don’t need to memorize the layers, but you’ll use tools like Wireshark to “see” what happens at each level later in the course.

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📦 3. What Are Data Packets?

When you send a message, it doesn’t travel as one big piece. The data is broken into small packets (usually 512–1500 bytes), and each packet travels separately to its destination.

Each packet contains:

• A header: includes source/destination IP, packet number, protocol
• A payload: the actual chunk of your data (e.g., part of a photo or message)
• A trailer: used for error checking

When all packets arrive, they are reassembled in the correct order.

Why use packets?

• Faster: packets take different paths and avoid slow links
• Reliable: if one packet is lost, only that part is resent
• Secure: easier to scan, inspect, or encrypt individual parts

💡 Tip: Think of packets like puzzle pieces. Each one matters — and they’re useless unless you put them together correctly.

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📘 4. What Is an IP Address?

An IP address (Internet Protocol address) identifies a device on a network. Every device connected to a network must have one.

There are two main versions:

• IPv4 (e.g., 192.168.1.1) — still the most common, but running out
• IPv6 (e.g., 2001:0db8:85a3:0000:0000:8a2e:0370:7334) — designed for the future

There are two types of IP addresses:

• Private: used inside your local network (192.168.x.x)
• Public: assigned by your internet provider and visible to the world

🔍 Use a tool like ipconfig (Windows) or ifconfig (Mac/Linux) to see your IP address.

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🧭 5. DNS: The Internet’s Phonebook

DNS (Domain Name System) translates human-friendly names like google.com into IP addresses that computers can understand.

When you type www.cyber-school.co.il:

1. Your device checks its cache (local memory)
2. If not found, it asks a recursive DNS server
3. The request travels through a hierarchy of DNS servers:
   • Root → Top Level Domain (TLD) → Authoritative server
4. The correct IP is returned and your browser connects to that address

⚠️ Hackers can poison or fake DNS responses — that’s why Cyber Rangers check DNS integrity!

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📡 6. Routers and Switches – The Traffic Directors

Switches work inside local networks:

• Learn device MAC addresses
• Send data only where needed (not to all devices)

Routers connect different networks:

• Choose the best path for packets
• Translate between private and public IP addresses (NAT)
• Often act as a firewall and basic security tool

🗺️ Every packet travels through multiple routers to reach its destination, sometimes crossing countries or continents.

🧠 Most internet slowdowns happen at router “hops” or undersea links.

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🔐 7. How Hackers Attack Networks

Here’s how cyber attackers exploit networks:

Attack Type	How It Works
Packet Sniffing	Hackers use tools to copy data packets as they travel through a network
DNS Spoofing	The attacker tricks your device into visiting a fake website
MITM (Man in the Middle)	The attacker secretly intercepts and modifies data between two parties
Unencrypted Traffic Theft	If traffic isn’t encrypted, anyone can read it on public Wi-Fi

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🛡️ 8. How Cyber Rangers Defend the Digital World

Defensive actions you’ll learn and practice:

• Encryption: Turns messages into unreadable code (TLS, HTTPS, VPN)
• Firewalls: Block unwanted traffic from entering the network
• Packet analysis: Using tools like Wireshark to inspect traffic
• Network monitoring: Look for anomalies or suspicious behavior
• DNS filtering: Block known malicious domains

These defenses are the backbone of network security in every industry.

✅ If you understand how data flows, you can learn where to protect it — and where to expect attackers.

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🔧 9. Technical Tools You’ll Encounter

Tool	What It Does
Packet Tracer	Cisco’s simulation tool to model networks and visualize data flow
Wireshark	A powerful analyzer that lets you see real packet data
ipconfig / ping / tracert	Basic diagnostic tools for IP and network paths
Browser Dev Tools (Network tab)	Shows requests your browser makes for each page

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🧠 Review & Practice Questions

1. What is the purpose of breaking data into packets?
2. What does a router do when it receives a packet?
3. Explain the difference between an IP address and a DNS name.
4. What might a hacker do with unencrypted traffic on public Wi-Fi?
5. How can encryption and firewalls protect your digital data?