Introduction to Networks#

First lesson. Foundation stuff. Network devices, clients, servers. Basic but important.

What Is a Network?#

Devices (nodes) that can talk to each other and share stuff. That’s it.

Common network devices:

  • Router
  • Switch
  • Firewall
  • Server
  • Client (End Host)

Clients and Servers#

Client - asks for stuff. Your phone opening YouTube = client.

Server - gives you stuff. YouTube’s servers = server.

A device can be both. PC1 asks PC2 for a file → PC1 is client, PC2 is server. Roles flip depending on who’s asking.

Examples:

  • Two PCs: PC1 wants image.jpg from PC2. PC1 = client, PC2 = server.
  • YouTube: Your device = client, YouTube = server.
  • AirDrop: Friend’s iPhone = server, your iPhone = client.

Switches#

Connect devices within the same LAN. Like a smart power strip.

  • Usually 24+ ports
  • Connect PCs, printers, servers in one place
  • Forward traffic within the same network
  • Can’t connect to Internet directly (router’s job)

Models: Cisco Catalyst 9200, Catalyst 3650

Office setup: computers plug into switch, switch lets PC1 talk to PC2 without Internet.

Routers#

Connect different networks. Office network to Internet, or New York office to Tokyo office.

  • Fewer ports than switches
  • Connect LANs to each other and Internet
  • Figure out best path for data (routing)

Example: NY and Tokyo offices. Each has router → local switch + Internet. Routers send data between offices through Internet.

Models: Cisco ISR 900, ISR 1000, ISR 4000

Firewalls#

Control traffic entering/leaving network based on rules. Like a bouncer.

Where they go:

  • Outside router (filter Internet traffic)
  • Inside network (filter internal traffic)
  • Sometimes both

What they do:

  • Watch traffic
  • Allow/block based on rules
  • Protect against attacks

Types:

  1. Network Firewalls (Hardware) - Physical devices

    • Cisco ASA 5500-X
    • Cisco Firepower 2100 (Next-Gen)

  2. Host-Based Firewalls (Software) - On your computer

    • Windows Firewall
    • Protects that device

Next-Generation Firewalls (NGFW) - fancy ones with IPS, Deep Packet Inspection, application awareness. Most modern Cisco firewalls are NGFWs.

How It All Works Together#

Typical setup:

  • End Hosts: PCs, servers, printers
  • Switches: Connect local network
  • Routers: Connect networks/Internet
  • Firewalls: Keep bad stuff out

Flow: PC1 (Client) → Switch → Router → Internet → Router → Switch → Server1

Quick Reference#

Thing What It Does
Network Connects devices so they can share stuff
Client Asks for services
Server Provides services
Switch Connects devices in the same LAN
Router Connects different LANs and the Internet
Firewall Controls traffic for security
LAN Your local network (home/office)
NGFW Fancy firewall with extra security features

Real World Example#

Connect 30 PCs? Use a switch.

Connect office network to Internet? Use a router.

Protect network? Use a firewall (preferably Next-Gen).

Every PC should have software firewall enabled too.