Day 1: Network Devices and Fundamentals

Networking Fundamentals

Core Concepts

What is a Network?

A network is a digital telecommunications system that allows nodes (devices) to share resources and communicate with each other.

Device Roles

Client

• A device that accesses services or resources provided by another device

• Initiates requests to servers

Server

• A device that provides services, functions, or resources to client devices

• Responds to client requests

Note: Devices are not inherently "client" or "server"—the same device can fulfill either role depending on the context. Example: In a peer-to-peer (P2P) network, all devices act as both clients and servers.

Network Devices by Function

Switches (OSI Layer 2)

Purpose: Connect devices within a single LAN

Key Characteristics:

• Multiple network ports/interfaces for connecting end hosts

• Operate at Layer 2 (Data Link Layer) of the OSI model

• Enable device-to-device communication on the same local network

• Forward frames based on MAC addresses

What they do NOT do:

• Provide connectivity between different LANs

• Route traffic over the Internet

• Connect networks to the wider world

Routers (OSI Layer 3)

Purpose: Connect multiple networks and route traffic between them

Key Characteristics:

• Fewer network interfaces than switches

• Operate at Layer 3 (Network Layer) of the OSI model

• Forward packets between LANs using IP addresses

• Enable communication across the Internet

• Can connect local networks to ISP networks

Firewalls (OSI Layers 3–7)

Purpose: Control and monitor network traffic to enforce security policies

Key Characteristics:

• Specialty network security devices that filter traffic entering and exiting a network

• Operate at multiple OSI layers depending on filtering sophistication

• Monitor and enforce rules based on traffic patterns, protocols, and applications

Types:

Network-based Firewalls

• Dedicated hardware devices placed at network perimeter (inside or outside)

• Protect entire networks

• Examples: Cisco ASA, Palo Alto Networks, Fortinet FortiGate

Host-based Firewalls

• Software applications running on individual machines

• Protect only that specific device (e.g., Windows Defender Firewall, macOS firewall)

• Examples: Personal computers, servers

Next-Generation Firewalls (NGFW)

• Enhanced firewalls with advanced filtering capabilities

• Include features like:

  • Application-layer awareness

  • Intrusion prevention

  • Deep packet inspection

  • User/identity-based policies

Summary Table