🧮 Subnet Calculator

What is Subnetting?

Subnetting is the process of dividing a larger IP network into smaller, more manageable sub-networks (subnets). It allows network administrators to efficiently allocate IP addresses, improve security by isolating network segments, and reduce broadcast traffic.

When you subnet a network, you borrow bits from the host portion of an IP address to create additional network addresses. Each subnet operates as an independent network, allowing you to control traffic flow between segments using routers and firewalls.

Why Subnet?

• Efficient IP allocation — Avoid wasting addresses by sizing subnets to actual need
• Improved security — Isolate sensitive systems into separate network segments
• Reduced broadcast traffic — Smaller subnets mean fewer devices receiving broadcast frames
• Simplified management — Organize your network logically by department, floor, or function
• Better performance — Less congestion and more predictable network behavior

CIDR Notation Explained

CIDR (Classless Inter-Domain Routing) notation is a compact way to represent an IP address and its associated subnet mask. It uses a forward slash followed by a number (e.g., /24) that indicates how many bits of the address are used for the network portion.

For example, 192.168.1.0/24 means the first 24 bits identify the network, leaving 8 bits for host addresses. This gives you 256 total addresses (254 usable hosts) in the subnet.

How It Works

An IPv4 address is 32 bits long. The CIDR prefix length tells you how many of those bits define the network:

• /8 — 8 network bits, 24 host bits → 16,777,214 hosts
• /16 — 16 network bits, 16 host bits → 65,534 hosts
• /24 — 24 network bits, 8 host bits → 254 hosts
• /30 — 30 network bits, 2 host bits → 2 hosts (point-to-point links)

CIDR replaced the older classful addressing system (Class A, B, C) and enables Variable Length Subnet Masking (VLSM), allowing networks to be divided into subnets of different sizes for maximum efficiency.