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Subnetting Based on Class IP Address: A Comprehensive Guide

Subnetting is a significant aspect of IP addressing, allowing us to divide larger networks into smaller subnetworks. In this blog post, we'll discuss how to perform subnetting based on class IP addresses.

Understanding Class IP Addresses

Classless Inter-Domain Routing (CIDR) has largely replaced the traditional concept of IP address classes. However, for understanding and working with IPv4 addresses, the class system is still widely used as a mental model. IP addresses are classified into five types: A, B, C, D, and E, based on their first few bits.

  • Class A: First octet ranges from 1 to 126 (8 bits for network address).
  • Class B: First octet ranges from 128 to 191 (14 bits for network address).
  • Class C: First octet ranges from 192 to 223 (6 bits for network address).
  • Class D: First octet is 224 (used for multicasting).
  • Class E: First octet is 225 to 239 (used for experimental purposes).

Subnetting Based on Class IP Addresses

The process of subnetting based on class IP addresses involves the following steps:

  1. Determine the default subnet mask for your IP address class.
  • Class A: Default subnet mask is 255.0.0.0 (8 bits for network, 24 bits for hosts).
  • Class B: Default subnet mask is 255.255.0.0 (14 bits for network, 16 bits for hosts).
  • Class C: Default subnet mask is 255.255.255.0 (6 bits for network, 22 bits for hosts).
  1. Calculate the subnet mask based on your desired subnet size.

The subnet mask's first X bits will be set to 1 (for the network), and the remaining bits will be set to 0 (for hosts). For example:

  • To create a subnet with 32 hosts: Mask for Class C: 255.255.255.224 (2 addresses for network + 30 addresses for hosts)
  • To create a subnet with 62 hosts: Mask for Class C: 255.255.255.192 (2 addresses for network + 62 addresses for hosts)
  1. Calculate the subnet and host addresses.

Using bitwise operations, determine the subnet address and the first available host address. For example:

  • IP Address: 192.168.1.0
  • Subnet Mask: 255.255.255.192

Subnet Address: 192.168.1.0 (no change) Network Address: 192.168.1.0 First Host Address: 192.168.1.63 Last Host Address: 192.168.1.127 Broadcast Address: 192.168.1.127 (note that only the last host is usable; the broadcast address should not be used for communication)

Conclusion

Understanding and practicing subnetting based on class IP addresses is an essential skill for any network professional. This comprehensive guide has walked you through the process, starting from understanding IP address classes to calculating subnets, subnet masks, and host addresses. With this knowledge, you'll be able to design and implement subnetworks in various scenarios effectively.

Published December, 2014