From Local Networks to the Internet
So far, you’ve learned many powerful Linux and operating system concepts:
users, permissions, processes, scripting, automation—and you’re already far ahead of most beginners.
However, one crucial concept is still missing before you truly feel like a Linux professional:
👉 Networking
In this article, we’ll build networking knowledge step by step, starting from your home network and ending with how the internet, DNS, firewalls, and ports actually work.
Local Area Network (LAN)
Let’s start with something familiar: your home network.
Your laptop, phone, printer, and smart TV are all connected to the same network.
This type of network is called a LAN (Local Area Network).
A LAN is:
A group of devices
Connected in the same physical location
Such as a house, office, school, or campus
Each device in a LAN must be uniquely identifiable.
IP Addresses — Identity of a Device
Every device on a network has a unique IP address.
IP stands for Internet Protocol.
Example:
172.16.0.0
An IPv4 address:
Is 32 bits long
Each bit is either
0or1Bits are grouped into 4 octets
Each octet = 8 bits
That’s why IP addresses range from:
0.0.0.0 → 255.255.255.255
Devices communicate by sending data to IP addresses, not names.
Switch — Communication Inside the LAN
Inside a LAN, devices communicate using a network switch.
A switch:
Knows all device IP addresses in the LAN
Forwards data to the correct destination
Example:
Your laptop sends data to the printer
The switch delivers it using the printer’s IP address
Router — Connecting to the Internet
What happens when you access Facebook or Google?
Those servers are outside your LAN.
This is where a router comes in.
A router:
Connects your LAN to the outside world
Bridges LAN and WAN (Wide Area Network)
Is your gateway to the internet
When your device sends data externally:
It sends the request to the router
The router forwards it to the internet
The response comes back the same way
The router’s IP address is called the gateway.
Subnets — Knowing What’s Local vs External
How does your device know whether an IP address is:
Inside the LAN?
Or outside on the internet?
This is determined by the subnet.
Subnet Mask Example
192.168.0.0 / 255.255.255.0
This means:
First 24 bits are fixed
Devices must start with
192.168.0Last octet can range from
0–255
CIDR Notation
Same subnet written as:
192.168.0.0/24
More examples:
/16→ first 16 bits fixed/24→ first 24 bits fixed
Subnet defines the IP address range of a LAN.
Required Network Information for a Device
To communicate properly, a device needs:
IP address
Subnet
Gateway
With this information:
LAN traffic goes through the switch
External traffic goes through the router
NAT — Network Address Translation
LAN IP addresses are private.
They are not visible on the internet.
When you send a request outside:
Your router replaces your private IP
Uses its public IP instead
This process is called NAT (Network Address Translation).
Why NAT Is Important
Security – internal devices are hidden
Efficiency – IP ranges can be reused
Multiple companies can use the same LAN IP ranges without conflict.
Firewalls — Controlling Access
By default, external devices cannot access your LAN.
This protection is enforced by a firewall.
A firewall:
Is a set of network rules
Controls who can access what
Protects against unauthorized traffic
You explicitly define:
Which IP addresses are allowed
Which services are accessible
Which ports are open
Ports — Doors to Applications
Every device has ports.
Think of ports like doors in a building:
Some doors are open
Some are closed
Some allow only specific guests
Applications listen on specific ports.
Common Standard Ports
80 → HTTP (web)
443 → HTTPS
3306 → MySQL
5432 → PostgreSQL
⚠️ Only one application can use a port at a time.
DNS — Translating Names to IPs
Humans don’t remember IP addresses.
We remember names like:
facebook.com
But networks only understand IP addresses.
This translation is done by DNS (Domain Name System).
DNS maps:
Domain name → IP address
Think of DNS as the internet’s address book.
Domain Hierarchy
DNS is hierarchical.
Top-Level Domains (TLDs)
.com– commercial.org– nonprofit.edu– education.gov– government.mil– military.net– networking
Country Domains
.de– Germany.us– United States.uk– United Kingdom.fr– France
Domain Management
All domain names are regulated by
Internet Corporation for Assigned Names and Numbers (ICANN).
ICANN:
Manages domain namespaces
Authorizes domain registrars
Ensures uniqueness worldwide
Subdomains
A company can create multiple services under one domain.
Example:
Each subdomain can:
Point to a different server
Have a different IP address
How DNS Resolution Works
When you type facebook.com:
Your OS sends a DNS request
Request goes to a recursive DNS server
If not cached:
Query root server
Then
.comserverThen authoritative name server
IP address is returned
Browser sends request to that IP
Results are cached to speed up future requests.
Useful Linux Networking Commands
ifconfig
Shows:
IP address
Subnet mask
Gateway
netstat
Shows:
Active connections
Listening ports
Network services
ps aux
Shows:
Running processes
Resource usage
Port information
nslookup
Domain → IP
IP → Domain
DNS server info
ping
Tests connectivity
Checks reachability
Why This Matters for DevOps
You don’t need to be a networking expert.
But with this foundation, you can:
Debug connection issues
Configure servers correctly
Understand cloud networking
Secure applications
Troubleshoot production outages
And throughout the bootcamp, you’ll use these concepts constantly.
Final Takeaway
Networking is the missing puzzle piece that connects:
Linux
Servers
Applications
The internet
