Subnetting Calculator

A Subnetting Calculator is a tool that helps network engineers and IT professionals perform subnetting calculations. Subnetting is the process of dividing an IP network into smaller, more manageable subnetworks (subnets). The calculator automates the process of calculating subnet-related information like the subnet mask, network address, broadcast address, and usable IP range based on an input IP address and subnet mask (CIDR notation).

Subnetting Calculator

Subnetting Calculator

Explanation of Key Columns:

  • CIDR Notation: The number after the / represents the length of the subnet mask (in bits). For example, /24 means that the first 24 bits of the IP address are reserved for the network portion, leaving the rest for host addresses.
  • Subnet Mask: The subnet mask in dotted decimal format, e.g., 255.255.255.0 corresponds to /24 in CIDR notation.
  • Total Subnets: The total number of subnets available for a given CIDR block.
  • Usable Hosts per Subnet: The number of usable host addresses within the subnet, calculated as 2^n - 2, where n is the number of host bits (the subtraction of 2 accounts for the network address and broadcast address).
  • Class: Indicates the IP address class: A, B, or C.
    • Class A addresses have the first octet ranging from 1 to 126 (default subnet mask /8).
    • Class B addresses range from 128 to 191 (default subnet mask /16).
    • Class C addresses range from 192 to 223 (default subnet mask /24).
  • Network Address Range: The range of IP addresses within the subnet, starting from the network address and ending at the broadcast address.
  • Broadcast Address: The last address in the range, used to broadcast data to all devices within the subnet.

How to Use This Chart:

  • CIDR Notation is useful for identifying the size of a network and the number of subnets or hosts available.
  • Subnet Mask is the key to understanding how much of the IP address is used for the network and how much is available for hosts.
  • Usable Hosts per Subnet will help when planning for the number of devices (hosts) that can be connected in a subnet.
  • This chart is especially helpful for network engineers or system administrators when planning IP address allocation for networks, subnets, and configuring routers, firewalls, and other devices.

Example:

If you are working with a Class C network and you want to know how many hosts you can assign to a subnet with a /24 subnet mask:

  • From the chart, a /24 subnet mask has 254 usable hosts.
  • The network range will be from 192.168.0.0 to 192.168.255.255, and the broadcast address will be 192.168.255.255.