Subnet Masks Lecture Notes

Introduction

• Topic: Subnet Masks

IP Address Basics

• Definition: An IP address is an identifier for a device on a network.
• Purpose: Required for communication.
• Focus: IPv4 address
  • 32-bit numeric address
  • Written as four numbers separated by periods (octets)
  • Each number ranges from 0 -255
• Components:
  • Network Address (Network ID)
  • Host Address (Host ID)
• Subnet Mask:
  • Resembles an IP address
  • Reveals the number of bits used for the network

IP Address and Subnet Mask Transformation

• Computers use binary format (1s and 0s)
• Using a bit octet chart to convert IP address and subnet mask to binary
  • Each bit in an octet can be either 1 or 0
  • Example given for conversion of 192.168.1.0 to binary
• Network Portion Identification
  • Subnet mask binary digit of 1 indicates network part
  • Masked portions reveal host portion
  • Examples provided with different subnet masks

Purpose of Network and Host Parts

• Manageability: Breaking down large networks into smaller sub-networks (subnetting)
  • Helps prevent network chaos and excessive traffic issues
  • Broadcasts between computers are confined within subnetworks, handled by routers
  • Routers intelligently route data between subnetworks

Subnetting

• Definition: Dividing a large network into smaller networks by changing the subnet mask
• Process:
  • Changing default subnet mask by borrowing bits from the host portion
  • Examples provided on how subnet masks change to create subnets
• Example:
  • Given: Small business with 12 computers (all on a single network)
  • Task: Break down into 3 smaller networks
  • Process involves borrowing bits from the default subnet mask
  • Result with different subnet masks and their corresponding subnets/hosts

IP Address Classes

• 5 Classes (A – E), but mainly A – C are used commercially
• Classes:
  • Class A: For large organizations (up to 16 million hosts)
  • Class B: For medium to large organizations (up to 65,000 hosts)
  • Class C: For small organizations/homes (up to 254 hosts)

CIDR Notation

• Definition: Classless Inter-Domain Routing, also known as slash notation
• Purpose: Shorter way to write a subnet mask
  • Example: /24 means the subnet mask is 24 bits in length

Conclusion

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