What Is a Network?
Understand what a network is, how LAN differs from WAN, key components, topologies, and the ARP protocol.
Learning Objectives
- → Define LAN, WAN, MAN, PAN and their ranges
- → Identify network components: NIC, Switch, Router, Access Point
- → Describe Star, Bus, and Ring topologies with trade-offs
- → Explain how ARP resolves IP addresses to MAC addresses
What Is a Network?
A computer network is a collection of devices (computers, servers, printers, phones) connected together to share resources and communicate. Without networks, every machine would be an isolated island.
Types of Networks
| Type | Full Name | Typical Range | Example |
|---|---|---|---|
| LAN | Local Area Network | Building / campus | Office WiFi |
| WAN | Wide Area Network | Country / continent | The Internet |
| MAN | Metropolitan Area Network | City | City fibre ring |
| PAN | Personal Area Network | < 10 m | Bluetooth headset |
LAN Deep Dive
A LAN (Local Area Network) connects devices in a limited geographic area — your home, a school floor, or a company building. Key properties:
- High speed — typically 100 Mbps to 10 Gbps
- Low latency — devices are physically close
- Privately owned — managed by you or your organisation
- Shared medium — all devices can communicate with each other
Core Network Components
[Laptop] ──┐
[Phone] ──┤── [Switch] ── [Router] ── 🌐 Internet
[Desktop]──┘
| Component | Role |
|---|---|
| NIC (Network Interface Card) | Gives a device a hardware address (MAC) to send/receive frames |
| Switch | Connects devices within a LAN, forwards frames using MAC addresses |
| Router | Connects different networks (LAN ↔ Internet), forwards packets using IP |
| Access Point (AP) | Extends the LAN wirelessly (WiFi) |
| Modem | Converts ISP signal (fibre/DSL/cable) to Ethernet for the router |
Network Models
Client–Server: A dedicated server provides services (files, web pages, email) and clients request them. Used in offices and the internet.
Peer-to-Peer (P2P): Each device can be both client and server. Common in small home networks and BitTorrent.
MAC vs IP Address
- MAC address — hardware-burned identifier, e.g.
00:1A:2B:3C:4D:5E. Used inside a LAN. - IP address — logical address assigned by software, e.g.
192.168.1.10. Used for routing between networks.
Think of MAC as your passport number (fixed identity) and IP as your hotel room (changes with location).
Key Takeaways
- Networks exist to share resources and enable communication.
- LAN = local, fast, private; WAN = long-distance, public.
- Switch handles LAN traffic; Router connects networks.
- Every device has a MAC (layer 2) and an IP (layer 3).
A computer network is a collection of devices — computers, servers, phones, printers — connected together to share resources and communicate.
| Type | Full Name | Typical Range | Example |
|---|---|---|---|
| LAN | Local Area Network | Building / Campus | Office WiFi |
| WAN | Wide Area Network | Country / World | The Internet |
| MAN | Metropolitan Area Network | City | City fibre ring |
| PAN | Personal Area Network | < 10 metres | Bluetooth headset |
What does LAN stand for?
Which network type spans an entire city?
Three core devices make a LAN work. Each operates at a different OSI layer and has a distinct role.
Hub
Broadcasts every packet to ALL ports. No intelligence — every device sees all traffic.
Switch
Learns which MAC is on which port. Sends frames ONLY to the correct destination.
Router
Connects different networks. Routes packets using IP addresses. Your home gateway.
| Device | OSI Layer | Address Used | Forwards To |
|---|---|---|---|
| Hub | 1 — Physical | None | ALL ports |
| Switch | 2 — Data Link | MAC address | Correct port only |
| Router | 3 — Network | IP address | Next hop / internet |
A Switch decides where to forward a frame using:
Which device operates at Layer 3 and routes between different networks?
Every device has two addresses serving different purposes — a MAC address for local delivery and an IP address for routing across networks.
🔵 MAC Address
- 48-bit (6 bytes) hardware ID
- Burned into the NIC by manufacturer
- Used within one LAN segment only
- Layer 2 — Data Link
🟢 IP Address
- 32-bit (IPv4) or 128-bit (IPv6)
- Assigned by DHCP or manually
- Used for routing between networks
- Layer 3 — Network
How many bits does an IPv4 address contain?
A MAC address is burned into the:
ARP bridges the gap between IP (Layer 3) and MAC (Layer 2). A device must know the target's MAC address before it can send a frame on the LAN.
Sent to FF:FF:FF:FF:FF:FF — all devices on the LAN receive it.
Only the device that owns that IP answers — directly back to the requester.
The mapping is stored in the ARP cache to avoid repeated broadcasts.
✖ ARP Spoofing
ARP has no authentication. Any device can send a fake ARP reply claiming to be the gateway. This is called ARP Spoofing and is the foundation of most LAN-based MITM attacks. Covered in depth in Lesson 2: LAN Security.
What MAC address does an ARP Request broadcast to?
ARP resolves an IP address into which type of address?
💪 Exercises & Challenges
LAN Concepts Quiz
Test your knowledge of topologies, devices, subnetting, ARP, and DHCP.
Identify the ARP Attack
Analyze an ARP cache and identify whether an attack is in progress.
Explore Your LAN
## Task: Map Your Local Network Use built-in tools to discover your own LAN configuration. ### Steps **Step 1 — Find your IP and MAC:** ```bash # Linux / Mac ip addr show # or: ifconfig # Wi
Network Recon Challenge
You are given access to a test LAN environment. Your goal is to identify the **default gateway** IP of the network `10.0.0.0/24` using only command-line tools. Run: `ip route show default` — the gate