Subnet Calculator

What is a Subnet Calculator?

A Subnet Calculator is an essential tool for network engineers, system administrators, and developers to plan and verify network configurations. It takes an IP address and a network mask (CIDR) and calculates the network range, broadcast address, and the number of usable hosts.

Whether you are configuring a VPC in AWS, setting up a home network, or preparing for a Cisco CCNA exam, understanding subnetting is crucial for efficient network design.

How Subnetting Works

Subnetting is the practice of dividing a single large network into smaller, manageable networks (subnets). This improves performance and security by reducing broadcast traffic.

Every IP address (IPv4) consists of 32 bits, split into 4 "octets". The Subnet Mask determines which part of the IP address represents the Network and which part represents the Host.

Understanding CIDR Notation

CIDR (Classless Inter-Domain Routing) is the modern way to represent subnet masks. It is written as a suffix, like /24. The number represents how many bits are turned "on" (set to 1) in the network mask.

• /24 = 255.255.255.0 (Standard Home Network, 254 hosts)
• /16 = 255.255.0.0 (Large Enterprise Network, 65k hosts)
• /8 = 255.0.0.0 (Massive Network, 16M hosts)
• /32 = 255.255.255.255 (Single specific IP host)

Key Terms Explained

• Network Address: The first address in the subnet. It identifies the subnet itself and cannot be assigned to a device.
• Broadcast Address: The last address in the subnet. Data sent to this address is received by all devices in that subnet.
• Usable Host Range: All the IP addresses between the Network and Broadcast addresses. These are the IPs you can actually assign to computers, printers, and servers.
• Wildcard Mask: The inverse of the subnet mask. Often used in Access Control Lists (ACLs) on routers (e.g., Cisco IOS).

IP Classes

Before CIDR, IP addresses were categorized into "Classes". While modern routing uses CIDR, these terms are still common in networking theory:

• Class A (0-127): For huge networks (Millions of hosts).
• Class B (128-191): For medium-sized networks.
• Class C (192-223): For small networks (LANs).

Why use RootUtils for Subnetting?

Unlike other tools, the RootUtils Subnet Calculator runs 100% in your browser. Your internal IP addresses are never sent to a server, ensuring total privacy for your infrastructure planning.