Lecture Notes: Detailed Calculation of Subnets and Hosts using IPv4

Introduction

• Importance of calculating IP addresses and subnet masks.
• Creation of smaller networks to facilitate global communication.
• Concept of routers enabling data transfer between networks.
• Introduction to Variable Length Subnet Masks (VLSM).

Overview of VLSM

• VLSMs provide flexibility unlike class-based networks with fixed subnet bits.
• Network administrators can design networks with the right number of hosts and networks.
• Analogy: Like cutting a pizza into the required number of pieces.

Class A Network Example

• Example network: 10.0.0.0 with a default subnet mask of 255.0.0.0 (/8).
• Explanation of classful vs. classless addressing.

Variable Length Subnet Masking

• Slash notation examples: /24, /26.
• Default subnet mask for Class A (255.0.0.0) explained in binary.
• Conversion and calculations: binary to decimal and CIDR notation.

Subnet and Host Calculation

• Use of powers of two for quicker calculations.
  • Subnets: 2^(number of subnet bits).
  • Hosts per subnet: 2^(number of host bits) - 2.
  • Subtraction accounts for network and broadcast addresses.

Example Calculations

Example 1: IP 10.1.1.0 /24

• Default Class A network has 8 network bits.
• Additional 16 bits borrowed for subnet, leaving 8 host bits.
• Calculations:
  • Number of Subnets: 2^16 = 65,536.
  • Hosts per Subnet: 2^8 - 2 = 254.

Example 2: IP 192.168.11.0 /26

• Class C address, default network bits: 24.
• 2 additional subnet bits, 6 host bits.
• Calculations:
  • Number of Subnets: 2^2 = 4.
  • Hosts per Subnet: 2^6 - 2 = 62.

Example 3: IP 172.16.55.0 /21

• Class B address, default network bits: 16.
• 5 additional subnet bits, 11 host bits.
• Calculations:
  • Number of Subnets: 2^5 = 32.
  • Hosts per Subnet: 2^11 - 2 = 2,046.

Conclusion

• Powers of two provide a quick method for subnet and host calculations.
• Upcoming videos will cover shortcuts for faster calculations.