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IP Addressing

An IP Address is a unique number assigned to every device in a network so it can be identified and communicate.

1. IP Address Basics

  • Example: 192.168.1.10 (IPv4)
  • Types:
    • Private IP — used inside local networks
    • Public IP — used on the internet
  • Versions:
    • IPv4 → 32-bit (like 192.168.1.1)
    • IPv6 → 128-bit (like fe80::1)
      IPv4 Structure

2. Localhost (Loopback)

Used to refer to your own computer

  • 127.0.0.1 → Localhost
  • Range: 127.0.0.0 – 127.255.255.255
  • Used for:
    • Testing
    • Development
    • No internet needed

3. Private IP Addresses

Used inside homes, offices, LAN networks. Not accessible directly from internet.

Class A Private Range

Used in big networks

Range 10.0.0.0 – 10.255.255.255
Examples:
  • 10.0.0.1
  • 10.10.10.10
  • 10.1.1.1

Class B Private Range

Used in medium networks

Range 172.16.0.0 – 172.31.255.255
Examples:
  • 172.16.0.1
  • 172.20.5.10
  • 172.31.100.50

    ❗ Only 172.16 → 172.31 are private. Other 172.x are public.

Class C Private Range

Most common in home WiFi

Range 192.168.0.0 – 192.168.255.255
Examples:
  • 192.168.0.1
  • 192.168.1.1
  • 192.168.43.1 (Hotspot)
    https://res.cloudinary.com/dwdbp4qpe/image/upload/v1772292339/private-and-public-IP_njikrv.png

4. Public IP

Used on the internet. Assigned by ISP.
Examples:

  • 8.8.8.8 (Google DNS)
  • 142.250.183.14
  • 52.95.245.123
    Anyone on internet can reach (unless blocked).

5. Special IP Ranges

APIPA (Automatic Private IP)

Assigned when no DHCP / WiFi problem

Range 169.254.x.x

Meaning:

  • Network problem
  • Failed to get IP

6. MAC Address

A MAC Address is a hardware identifier burned into the network card by the manufacturer.

Feature Description
Example A4:B3:22:1F:9C:10
Layer Data Link Layer
Size 48-bit address
Changes Never (normally)

Remember: MAC = Physical identity, IP = Logical identity

IP vs MAC

Feature IP Address MAC Address
Type Logical identifier Physical identifier
Layer Network Layer Data Link Layer
Assigned by Network/ISP Manufacturer
Changes Yes (dynamic) No (hardware)

7. Subnetting

Subnetting divides a large network into smaller networks.

Why Subnet?

  • Better performance
  • Improved security
  • Efficient IP usage

Example

Network: 192.168.1.0/24
Subnetted into:

  • 192.168.1.0/26
  • 192.168.1.64/26
  • 192.168.1.128/26
  • 192.168.1.192/26

8. CIDR Notation

CIDR = Classless Inter-Domain Routing
Represents network mask.

CIDR Subnet Mask Hosts
/24 255.255.255.0 254
/16 255.255.0.0 65,534
/32 255.255.255.255 1 (single IP)
/8 255.0.0.0 16,777,214

9. NAT (Network Address Translation)

NAT converts Private IP ↔ Public IP

Uses

  • Security
  • Limited IPv4 saving
  • Home routers

Types of NAT

Type Description
Static NAT One-to-one mapping
Dynamic NAT Pool of public IPs
PAT Port Address Translation (many-to-one)

https://res.cloudinary.com/dwdbp4qpe/image/upload/v1772292339/Pasted_image_20260202225457_tlm7z1.png

10. Useful Commands

Show IP Addresses

ip addr

Show Neighbors (ARP Table)

ip neigh

Show Routing Table

ip route

Find Public IP

curl ifconfig.me

Force IPv4 or IPv6

curl -4 ifconfig.me
curl -6 ifconfig.me

11. Quick Reference

IP Type Range Use Case
Class A Private 10.0.0.0/8 Large networks
Class B Private 172.16.0.0/12 Medium networks
Class C Private 192.168.0.0/16 Home/Small networks
Loopback 127.0.0.0/8 Local testing
APIPA 169.254.0.0/16 No DHCP available