Subnetting in Classful Addressing

Introduction

• Welcome to Gate Smashers.
• Today's topic: Subnetting in Classful Addressing.
• Discussing different classes of IP addresses: A, B, C, D, E.

What is Subnetting?

• Definition: Dividing a big network into smaller networks (subnets).
• Purpose:
  • Easier maintenance of large networks.
  • Improved organization within large entities (e.g., universities, organizations).

Example Scenario

• Example: A large university with diverse departments (examinations, placements, academics, etc.).
• Problem: Managing many hosts (e.g., Class A can have millions) is difficult.
• Solution: Subnetting helps to logically divide the network into manageable parts.

Advantages of Subnetting

1. Ease of Maintenance:
   • Dividing the network allows for dedicated administration.
2. Enhanced Security:
   • Separate subnets for departments can improve security and authorization for hosts.

How Subnetting is Done

• Example Network: Class C with address 200.10.20.0.
  • Class C range: 190-223.
  • Total possible hosts: 256.
  • Usable hosts: 254 (excluding network ID and broadcast address).
• Dividing Into Subnets:
  • Aim to divide into two logical parts.
  • Do not disturb the first three octets; modify only the last octet.

Subnetting Process

1. Fixing the Network Bit:
   • Reserve 1 bit for subnetting (e.g., 200.10.20.0 and 200.10.20.128).
2. Last Octet Variations:
   • Keep the first bit (MSB) fixed for subnet 1; it’s 0 for subnet 1 and 1 for subnet 2.
3. Calculate Ranges:
   • Subnet 1: 200.10.20.0 to 200.10.20.127 (Broadcast: 127).
   • Subnet 2: 200.10.20.128 to 200.10.20.255 (Broadcast: 255).
4. Total Hosts:
   • Each subnet has 128 total addresses, with 126 usable after accounting for network ID and broadcast address.

Important Addresses

• Subnet IDs:
  • S1: 200.10.20.0
  • S2: 200.10.20.128
• Total Usable IPs:
  • Without subnetting: 254
  • With subnetting: 252 (126 usable per subnet).

Subnet Mask and Routing

• Default Subnet Mask for Class C: 255.255.255.0
• Subnet Mask after Subnetting: 255.255.255.128 (1 reserved bit).
• Routing:
  • Internal routing depends on subnet mask to determine destination subnet.

Disadvantages of Subnetting

• Increased complexity in finding network IDs, subnets, and hosts:
  • More steps to locate a specific host (network ID -> subnet -> host).
• Overall complexity increases but leads to easier management and enhanced security.

Conclusion

• Subnetting improves management and security of large networks.
• Understanding subnetting is crucial for efficient network administration.