“A subnetwork or subnet is a logical subdivision of an IP network. The practice of dividing a network into two or more networks is called subnetting.”

Subnetting improves efficiency by “reducing network traffic by traveling shorter distances” and “avoiding unnecessary routes, therefore, shortening the destination path.”

IP Address and Subnet Mask

IPv4 addresses consist of 32 binary bits divided into network and host portions. “The range of values in decimal is 0 to 255 because that represents 00000000 to 11111111 in binary.”

Subnet High Level View

Class A Network:

  • Public IP Range: 1.0.0.0 to 127.0.0.0
  • First octet value range: 1 to 127
  • Subnet Mask: 255.0.0.0 (8 bits)
  • Number of Networks: 128
  • Number of Hosts per Network: 16,777,214
  • Format: N.H.H.H

Example: “10.14.1.57” (network: “10”, device ID: “14.1.57”)

Class B Network:

  • Public IP Range: 128.0.0.0 to 191.255.255.255
  • First octet value range: 128 to 191
  • Subnet Mask: 255.255.0.0 (16 bits)
  • Number of Networks: 16,384
  • Number of Hosts per Network: 65,534
  • Format: N.N.H.H

Example: “172.16.25.122” (network: “172.16”, device ID: “25.122”)

Class C Network:

  • Public IP Range: 192.0.0.0 to 223.255.255.255
  • First octet value range: 192 to 223
  • Subnet Mask: 255.255.255.0 (24 bits)
  • Number of Networks: 2,097,152
  • Number of Hosts per Network: 254
  • Format: N.N.N.H

Example: “192.168.114.109” (network: “192.168.114”, device ID: “109”)

Subnet Classes

Classful Subnetting Definitions

  • “Network address – All 0’s in the host portion of an address”
  • “Broadcast address – All 1’s in the host portion of an address”

Why Use Subnetting?

Subnetting addresses network speed challenges by “separating larger networks into smaller networks. Consequently, reducing congestion and better data flow.”

Additional benefits include:

  • Efficient IP address allocation
  • Logical network division for administrative purposes
  • Enhanced security through access controls between subnets
  • Containment of malware spread

Subnetting Rule of Thumb

The article references the “Seven Second Subnetting Rule” by Professor Messer, a helpful video tutorial for quickly working out subnet math.

The Bottom Line

Subnetting “helps to efficiently allocate IP addresses. Therefore, prevents large numbers of IP addresses from going unused” and “improving performance and network security.”