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Kervie Sazon
Kervie Sazon

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Networking Fundamentals - Part 1: IP Addressing

#beginners #computerscience #networking #tutorial

What is IP Address?

An IP Address is like a home address for a computer on a network.

Just like:

  • Mail needs an address to arrive.
  • Data needs an IP Address to reach the right computer.

Example:

192.168.1.10
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This number uniquely identifies a computer inside a network.

IPv4 vs IPv6

IPv4

The most commonly used IP addressing system in current networks, including servers and local networks.

Looks like:

192.168.1.10 

or

10.0.0.5
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Uses numbers only.

IPv6

A newer version of IP that provides a much larger number of addresses than IPv4, allowing more devices to connect to the internet.

Looks like:

2001:0db8:85a3::8a2e:0370:7334
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That's how IPv6 looks (for awareness).

Public IP vs Private IP

Private IP Addresses

It is used inside a private networks.

Common private ranges:

10.0.0.0 – 10.255.255.255
172.16.0.0 – 172.31.255.255
192.168.0.0 – 192.168.255.255
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Public IP Addresses

  • Used on the internet.
  • Must be unique worldwide.

Simple rule to remember:
If it starts with 10., 172.16–31, or 192.168., it’s PRIVATE.

Example:
The server has a private IP, so it can't be accessed directly from the internet.

Static IP vs Dynamic IP

Static IP

  • Does not change.
  • Manually asigned.

Dynamic IP

  • Can change over time.
  • Assigned automatically.

Why this matters?

Servers usually need static IPs so apps always know where to connect.

Example:
“The app broke because the server got a new IP address.”

IP Address Structure

IPv4 format 

192.168.1.10
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This has:

  • 4 number which is called (Octets).
  • Each number is between 0 - 255.

CIDR Notation

what this means?

You might see:

192.168.1.10/24
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Simple explanation
/24 describes how big the network is.
It's the most common size.

/24 = typical local network.

Loopback Address (Special IP)

What it is?

127.0.0.1
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What it means

  • Refers to our own computer.
  • Used for testing.

Example:
“I tested the app locally using 127.0.0.1.”

How to view IP Addresses in Linux

Command: 

ip addr
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What to look for:

Look for Interface name:
lo - Loopback.
eht0 , eht1 - Wired network (Ethernet). Servers & VMs.
wlan0 - Wireless (Wi-Fi). Common on laptops.
ens33 , enp0s3 - Still Ethernet. Just different naming style.
docker0 - Created by docker. Used for containers.

Look for inet - IPv4 address.

Look for UP - Interface is active.

Example 1:

1: lo: <UP,LOOPBACK>
    inet 127.0.0.1/8

2: eth0: <UP>
    inet 10.0.0.15/24
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Junior conclusion:
“The server is online and has a private IP address on interface eth0.”

Example 2: Interface is Down(Problem Case)

2: eth0: <DOWN>
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This means the network interface is off, no IP Address and no network connectivity.

The explanation in this is:
“The server doesn’t have network connectivity because the main interface is down.”

Example 3: No IP Address Assigned

2: eth0: <UP>
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No inet line. Meaning, interface is UP but no IP Address.

The explation in this case is:
"The interface is up, but it hasn’t been assigned an IP address.”

Example 4: Multiple Interfaces

1: lo: <UP>
    inet 127.0.0.1/8

2: eth0: <UP>
    inet 10.0.0.15/24

3: eth1: <UP>
    inet 192.168.1.20/24
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The server has two network connections. Two different networks.

Understanding:
eth0 - internal network.
eth1 - another network (maybe management or backup).

The explanation in this is:
"The server has multiple active network interfaces connected to different networks.”

Example 5: Wi-Fi interface (Laptop)

3: wlan0: <UP>
    inet 192.168.0.101/24
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This means wlan0 = WI-fi. Private IP. Home or office network.

What to look for:

When seeing ip addr ask:

  1. What is the interface name?
  2. Is it UP or DOWN?
  3. Does it have an inet (IPv4) address?
  4. Is the IP private or public?
  5. Is this the interface used for network access?

Today, I learned what an IP address is and how it helps computers identify and communicate with each other on a network. I understood that IPv4 is the most commonly used IP addressing system, while IPv6 exists to support a growing number of devices. I also practiced using the ip addr command in Linux to identify network interfaces and check assigned IP addresses.

Tomorrow, I’m going to study Subnetting and CIDR to better understand how networks are divided and organized.

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