Understanding Networking Fundamentals: IP Addresses, Subnets, and CIDR

1. IP Addresses: The Foundation

What is an IP Address?

• An IP address is a unique identifier assigned to devices connected to a network

• Helps in tracking, monitoring, and controlling access for specific devices

• Essential for network management and security

IPv4 Address Structure

• Consists of 4 bytes (32 bits)

• Each byte is separated by dots (e.g., 192.168.1.1)

• Each number can range from 0 to 255

• Format: x.x.x.x where x ∈ [0,255]

Binary Representation

• Each byte represents 8 bits

• Maximum value: 11111111 (binary) = 255 (decimal)

• Example conversion:

  • 192 = 11000000 (binary)

  • Calculation: 2^7 + 2^6 = 128 + 64 = 192

2. Subnetting: Network Segmentation

What is a Subnet?

• A logical division of a larger network

• Allows for better organization and security

• Helps isolate network traffic and control access

Types of Subnets

1. Private Subnet

   • No direct internet access

   • Used for internal resources

   • Greater security

2. Public Subnet

   • Has internet access

   • Connected through internet gateway

   • Used for public-facing resources

Benefits of Subnetting

• Enhanced security through isolation

• Better network organization

• Improved network performance

• Easier network management

3. CIDR (Classless Inter-Domain Routing)

Understanding CIDR Notation

• Format: IP_Address/prefix_length

• Example: 172.16.3.0/24

• Prefix length ranges from 0 to 32

CIDR Calculation

1. Formula: Available IP addresses = 2^(32 - prefix_length)

2. Common prefix lengths:

   • /24 = 256 addresses (2^8)

   • /26 = 64 addresses (2^6)

   • /27 = 32 addresses (2^5)

   • /28 = 16 addresses (2^4)

Private IP Address Ranges

• 10.0.0.0/8 (Class A)

• 172.16.0.0/12 (Class B)

• 192.168.0.0/16 (Class C)

4. Network Ports

Understanding Ports

• Unique numbers assigned to applications on a device

• Range: 0-65535

• Format: IP_Address:Port_Number

Common Port Numbers

• Some ports are reserved for specific services:

  • 80: HTTP

  • 443: HTTPS

  • 3306: MySQL

  • 8080: Often used for development servers

  • Custom applications should use non-standard ports (e.g., 9000, 9191)

Best Practices

1. IP Address Assignment

   • Use private IP ranges for internal networks

   • Plan subnet sizes based on expected growth

   • Document IP address allocation

2. Subnet Design

   • Separate sensitive resources into different subnets

   • Use appropriate subnet sizes to avoid waste

   • Consider future scaling needs

3. Port Usage

   • Avoid using well-known ports for custom applications

   • Document port assignments

   • Consider security implications when opening ports

Practical Example

Creating a VPC with subnets:

1. Create VPC with CIDR 172.16.0.0/16 (65,536 addresses)

2. Create finance subnet: 172.16.3.0/24 (256 addresses)

3. Create general subnet: 172.16.4.0/24 (256 addresses)

This structure provides:

• Clear network separation

• Adequate IP addresses for each segment

• Room for future expansion