Domain 4 — Network Security

Types of Networks

• LAN (Local Area Network): Limited geographic area — a floor, building, or campus
• WAN (Wide Area Network): Long-distance connections between geographically separated networks
• WLAN (Wireless LAN): A LAN using wireless connections (Wi-Fi)
• VPN (Virtual Private Network): A secure point-to-point connection over an untrusted network
• MAN (Metropolitan Area Network): Covers a city or metropolitan region
• PAN (Personal Area Network): Very short range — Bluetooth devices around a person
• SAN (Storage Area Network): High-speed network dedicated to storage devices

Network Devices

• Hubs: Broadcast all traffic to every connected device. Inefficient and a security liability. Rarely used in modern environments.
• Switches: Send traffic only to the intended recipient via MAC address. Can create VLANs. More efficient and more secure than hubs.
• Routers: Connect different networks and determine the most efficient path for traffic. Operate at Layer 3 (Network Layer) of the OSI model.
• Firewalls: Filter traffic based on defined rules. Deployed at the perimeter and internally to segment network zones.
• Servers: Provide services to other network devices — web, email, database, file servers.
• Endpoints: The end devices — desktops, laptops, tablets, mobile phones. Often the primary attack surface.

The OSI Model

The OSI model divides network communication into 7 distinct layers. As data moves down the stack, each layer adds a header — this is encapsulation. As data moves back up at the receiving end, each layer removes its header — this is de-encapsulation.

Mnemonic (top to bottom): All People Seem To Need Data Processing