A computer becomes useful in a connected world when it can communicate with other devices.

But when we say “connect a computer to a network,” several different concepts are involved.

You might connect your computer using Ethernet. That connection may place your computer inside a LAN. That LAN may connect to a WAN. The organization may operate an Intranet. It may provide selected external access through an Extranet. And the network may ultimately connect to the Internet.

These terms describe different aspects of networking.

1. Ethernet - How the Computer Connects

Ethernet is a family of wired networking technologies used to connect devices over a local network.

A typical connection looks like:

Computer
   │
   │ Ethernet cable
   ▼
Switch
   │
   ├── Computer
   ├── Printer
   └── Server

An Ethernet network uses technologies defined primarily by the IEEE 802.3 standards.

Your computer's Ethernet interface has a MAC address, which operates at the Data Link Layer (Layer 2) of the OSI model.

Modern Ethernet commonly provides speeds such as:

100 Mbps
1 Gbps
2.5 Gbps
10 Gbps
40/100+ Gbps in data-center environments

Why use Ethernet?

Ethernet provides:

High and predictable bandwidth
Low latency
Reliable wired connectivity
Full-duplex communication
Good security compared with an openly accessible wireless medium
Excellent performance for servers and infrastructure

For example, a developer's workstation might connect to the office switch using Ethernet.

Ethernet answers:

How is my device physically connected to the network?

2. LAN - The Local Network

A LAN (Local Area Network) connects devices within a limited geographical area such as:

A home
Office
School
Building
Campus

For example:

              LAN
     ┌─────────────────────┐
     │                     │
 PC ─┤                     │
     │      Ethernet       │
Laptop ──── Switch ─── Server
     │                     │
Printer ───────────────────┘

A LAN can use both Ethernet and Wi-Fi.

So:

Ethernet ≠ LAN

Ethernet is a networking technology. LAN describes the network's local scope.

A Wi-Fi network can also be a LAN.

Why use a LAN?

A LAN allows devices to:

Communicate with each other
Share files
Access printers
Access local servers
Share applications
Access databases
Reach the Internet through a gateway

For example, an office may have hundreds of computers connected to the same corporate LAN.

LAN answers:

Which devices are connected within my local environment?

3. WAN - Connecting Networks Across Distance

A WAN (Wide Area Network) connects networks across large geographical distances.

For example:

Office A LAN
     │
     │
     ▼
  Router
     │
     │ WAN
     │
     ▼
  Router
     │
     ▼
Office B LAN

A WAN can connect:

Different offices
Different cities
Different countries
Different data centers

Technologies used to build WAN connectivity can include:

MPLS
SD-WAN
Internet-based VPNs
Dedicated fiber connections
Carrier Ethernet
Leased lines
Cellular connectivity

A multinational company might connect its Pune, London and New York offices through a corporate WAN.

Why use a WAN?

A WAN allows an organization to operate as one connected network even when its locations are geographically separated.

It can provide:

Inter-office communication
Access to centralized applications
Data-center connectivity
Remote access to corporate resources
Disaster-recovery connectivity
Distributed application infrastructure

WAN answers:

How do I connect networks that are geographically far apart?

4. Intranet - The Organization's Private Network

An Intranet is a private network or set of private services operated by an organization for its internal users.

For example:

Employees
    │
    ▼
Corporate Network
    │
    ├── HR Portal
    ├── Internal Git
    ├── Jira
    ├── Internal APIs
    ├── Databases
    └── File Servers

The important concept here is access control.

An intranet is not simply defined by whether the network is physically inside an office.

A company's internal applications may be hosted in cloud infrastructure and still be part of its private corporate environment.

Employees may access these systems through:

Office LAN
Corporate WAN
VPN
Zero-trust access mechanisms

Why use an Intranet?

An organization can use an intranet for:

Internal applications
Employee portals
Documentation
Internal communication
Source-code repositories
Business systems
Internal APIs
Private databases

The benefit is controlled access to organizational resources.

Intranet answers:

Which network resources are intended primarily for our organization's internal users?

5. Extranet - Controlled Access for External Parties

An Extranet extends selected organizational resources to trusted external parties.

For example:

                    Company
                       │
             ┌─────────┴─────────┐
             │                   │
        Internal Users       External Partners
             │                   │
             ▼                   ▼
          Intranet            Extranet
                                 │
                       ┌─────────┼─────────┐
                       │         │         │
                    Supplier  Customer  Partner

A supplier might need access to a company's:

Order-management system
Inventory information
Procurement portal
APIs
Shipment information

But that supplier should not receive unrestricted access to the company's internal network.

The organization therefore exposes only the resources that the external party is authorized to use.

This can be implemented using technologies such as:

VPNs
Firewalls
Identity and access management
API gateways
Private connectivity
Zero-trust architectures
Application-level access controls

Why use an Extranet?

It allows organizations to collaborate securely with:

Suppliers
Customers
Vendors
Business partners
Contractors

without giving them complete access to the internal environment.

Extranet answers:

How can trusted external parties access selected organizational resources?

6. Internet - The Global Network of Networks

The Internet is a global system of interconnected networks.

It connects millions of networks operated by different organizations around the world.

At its foundation are technologies and protocols such as:

IP
TCP
UDP
DNS
BGP
HTTP/HTTPS
Ethernet
Fiber
Wireless technologies

A simplified view is:

Your Computer
     │
     ▼
Home / Office LAN
     │
     ▼
Router
     │
     ▼
ISP
     │
     ▼
Internet
     │
 ┌───┼───────────────┐
 ▼   ▼               ▼
Web  Cloud         Other Networks

Your computer usually does not directly connect to the entire Internet.

It connects to a local network.

That network connects through a router or gateway to an ISP (Internet Service Provider).

The ISP connects to other networks through the Internet's global routing infrastructure.

Why use the Internet?

The Internet enables:

Web applications
Email
Cloud computing
Video conferencing
Online banking
Streaming
APIs
Software distribution
Remote services
Global communication

Internet answers:

How can networks around the world communicate with one another?

Putting Everything Together

These concepts become much easier when viewed as layers of a real-world scenario.

Imagine you are working from home.

Your laptop connects to your home router using Wi-Fi or Ethernet.

Laptop
   │
   │ Ethernet / Wi-Fi
   ▼
Home LAN
   │
   ▼
Home Router
   │
   │ ISP connection
   ▼
Internet

Now imagine you are working for a company.

Your laptop might connect to:

Laptop
   │
   ▼
Office LAN
   │
   ▼
Corporate WAN
   │
   ├────────── Data Center
   │
   ├────────── Cloud
   │
   └────────── Other Offices

The organization may then provide:

                    Corporate Network
                           │
             ┌─────────────┴─────────────┐
             ▼                           ▼
         Intranet                    Extranet
             │                           │
       Employees                 Partners / Suppliers
             │
             ▼
      Internal Applications

And the company can also connect to the public Internet:

Corporate Network
       │
       ▼
   Firewall / Gateway
       │
       ▼
    Internet
       │
       ├── Public Websites
       ├── Cloud Services
       ├── SaaS
       └── External APIs

The Important Distinction

One of the easiest ways to understand networking is to stop treating these six terms as alternatives.

They describe different dimensions:

Concept	What it describes	Example
Ethernet	Networking technology	Ethernet cable + switch
LAN	Local network scope	Office network
WAN	Wide-area network connectivity	Pune ↔ London offices
Intranet	Private organizational environment	Internal HR portal
Extranet	Controlled external access	Supplier portal
Internet	Global interconnected network	Websites, cloud services

So a single computer can participate in several of these at the same time.

For example:

Your laptop → Ethernet → Office LAN → Corporate WAN → Internet

And through that corporate environment, you might access:

Intranet → Internal company applications

Extranet → A partner's authorized system

From a Computer to the Internet

Ultimately, networking can be viewed as a journey:

Application
    │
    ▼
Computer
    │
    ▼
Network Interface
    │
    ▼
Ethernet / Wi-Fi
    │
    ▼
LAN
    │
    ▼
Router / Gateway
    │
    ▼
WAN / ISP Network
    │
    ▼
Internet
    │
    ▼
Remote Network
    │
    ▼
Server / Application

This journey is the foundation on which modern systems are built.

When we later study DevOps, Kubernetes, microservices, cloud architecture and distributed systems, these networking fundamentals become essential.

A Kubernetes pod communicating with another pod, a microservice calling an API, a load balancer routing traffic, or a browser connecting to a cloud application are all built on top of these fundamental networking concepts.