Network Fundamentals // Lesson 02

Network
devices.

A network is more than switches and routers. In this lesson we'll look at the common devices that make up a modern network, what each one actually does and where it fits into the OSI model.

📖 Beginner ⏱ About 15 minutes ✓ Quiz included CCNA 200-301
01 // The big picture

Different devices solve different networking problems

A typical network might contain switches, routers, firewalls, wireless access points, servers and user devices. Some devices move traffic, some provide services and some enforce policy.

The easiest way to learn them is to ask: what decision does this device make?

Useful shortcut: a Layer 2 switch primarily makes forwarding decisions using MAC addresses, while a router makes forwarding decisions using IP addresses.
02 // Core devices

Devices you should recognise

Layer 3
🌐

Router

Connects different IP networks and forwards packets based on a routing table.

  • Uses destination IP addresses
  • Connects different subnets
  • Often acts as a default gateway
  • May provide NAT, ACLs or VPN services
Layer 2
🔀

Layer 2 Switch

Connects Ethernet devices within a LAN and forwards frames based on MAC addresses.

  • Learns source MAC addresses
  • Builds a MAC address table
  • Forwards frames within VLANs
  • Supports VLANs, trunks and STP
Layer 2 + 3
⚡

Layer 3 Switch

Combines high-speed Ethernet switching with IP routing capability.

  • Can route between VLANs
  • Uses switched virtual interfaces
  • May run dynamic routing protocols
  • Common in campus networks
Layers 3–7
🛡️

Firewall

Controls traffic between security zones according to policy.

  • Permits or denies traffic
  • Tracks connection state
  • May inspect applications
  • Often provides VPN and NAT services
Layer 2
📶

Wireless Access Point

Allows wireless clients to join a network and bridges wireless traffic into the wired LAN.

  • Advertises wireless networks
  • Uses 802.11 Wi-Fi standards
  • Maps wireless clients into VLANs
  • May be standalone or controller-managed
Management
🎛️

Wireless LAN Controller

Centrally manages multiple wireless access points and their configuration.

  • Centralises WLAN settings
  • Coordinates AP behaviour
  • May assist roaming
  • Simplifies large wireless deployments
Application
🖥️

Server

Provides services or resources to other devices on the network.

  • DNS servers resolve names
  • DHCP servers assign addressing
  • Web servers provide HTTP/HTTPS content
  • Authentication servers validate users
End host
💻

Endpoint

A device that originates or receives network traffic.

  • Laptops and desktops
  • Phones and tablets
  • Printers and cameras
  • IoT devices
03 // Compare

Switch vs router

This comparison is worth getting comfortable with early because it appears throughout CCNA.

Layer 2 Switch

Decision Destination MAC address
Table MAC address table
Main job Forward frames within a LAN or VLAN
PDU Ethernet frame
Broadcasts Normally forwarded within the VLAN

Router

Decision Destination IP address
Table Routing table
Main job Forward packets between IP networks
PDU IP packet
Broadcasts Does not normally forward Layer 2 broadcasts
04 // Follow the traffic

Laptop to web server

Imagine a laptop is browsing to a web server located on another IP network.

01
Laptop

The endpoint creates the application traffic and determines that the destination IP is not on its local subnet.

02
Access Switch

The switch forwards the Ethernet frame toward the default gateway based on the destination MAC address.

03
Router / L3 Switch

The Layer 3 device examines the destination IP address, consults its routing table and forwards the packet toward the remote network.

04
Firewall

If traffic crosses a security boundary, a firewall may inspect the connection and decide whether policy permits it.

05
Web Server

The server receives the connection and the web application processes the request.

05 // Power over Ethernet

Data and power on the same cable

Power over Ethernet allows an Ethernet connection to carry electrical power as well as data. This reduces the need for separate power supplies near network devices.

Wireless APs

Ceiling-mounted access points are commonly powered directly from a PoE-capable switch.

IP Phones

VoIP handsets can receive network connectivity and power over a single Ethernet cable.

IP Cameras

PoE makes it easier to install cameras in locations without nearby mains power.

Terminology: the device supplying power is the Power Sourcing Equipment (PSE). The device receiving the power is the Powered Device (PD).
06 // Practical thinking

A small office example

Imagine an office with 40 PCs, several phones, wireless access points, printers and an Internet connection.

You might use an access switch to connect PCs, printers and phones. The switch could also provide PoE to phones and wireless access points.

A Layer 3 switch could provide inter-VLAN routing between user, voice and management networks.

A firewall at the edge could enforce security policy, perform NAT and provide VPN connectivity.

Servers could provide services such as DNS, DHCP, authentication and applications, while a wireless controller or cloud platform could manage the access points.

07 // Check your knowledge

Quick quiz

1. Which value does a Layer 2 Ethernet switch primarily examine when forwarding a frame?

A Layer 2 switch forwards Ethernet frames primarily according to the destination MAC address and its MAC address table.

2. Which device is primarily responsible for forwarding packets between different IP networks?

Routers operate at Layer 3 and use routing information to forward IP packets between networks.

3. Which device would commonly act as the default gateway for a VLAN?

The default gateway must be able to route traffic outside the local IP subnet, so it is normally provided by a router or Layer 3 switch.

4. Which statement best describes a firewall?

Firewalls enforce security policy by permitting, denying or inspecting traffic crossing security boundaries.

5. In PoE terminology, what is the device receiving power called?

The Powered Device (PD) receives power. The Power Sourcing Equipment (PSE), such as a PoE switch, provides it.

6. Which device bridges wireless clients into the wired LAN?

A wireless access point provides 802.11 wireless connectivity and bridges client traffic into the wired network.
Score: 0 / 6
Lesson complete

Next: Ethernet, cabling & interfaces

Next we'll move down to the physical side of networking and look at copper, fibre, Ethernet speeds, duplex, connectors and interface types.