What is CIDR notation?

CIDR (Classless Inter-Domain Routing) notation like /24 represents the number of bits used for the network portion of an IP address. A /24 means the first 24 bits are the network, leaving 8 bits (256 addresses) for hosts.

What's the difference between network and broadcast address?

The network address is the first address in a subnet (all host bits are 0) and identifies the network itself. The broadcast address is the last address (all host bits are 1) and is used to send messages to all hosts on the subnet.

Why can't I use the network and broadcast addresses for hosts?

The network address identifies the subnet itself, and the broadcast address is reserved for sending data to all hosts. That's why usable hosts = total hosts - 2 (except for /31 and /32 subnets which have special uses).

What is a wildcard mask?

A wildcard mask is the inverse of a subnet mask. It's used in access control lists (ACLs) and routing protocols like OSPF. Where a subnet mask has 1s, the wildcard has 0s, and vice versa.

What are private IP address ranges?

Private IP ranges are: 10.0.0.0/8 (Class A), 172.16.0.0/12 (Class B), and 192.168.0.0/16 (Class C). These can be used on internal networks and aren't routable on the public internet.

Technology Calculators

Subnet Calculator (CIDR)

Calculate subnet masks, network addresses, broadcast addresses, usable host ranges, and IP address allocations from IP addresses and CIDR notation (/24, /16, etc.) for comprehensive network planning. Features IPv4 and IPv6 support, binary conversions, subnet splitting, supernetting analysis, and network capacity planning. Essential for network administrators, IT professionals, system engineers, and cybersecurity specialists designing networks, troubleshooting connectivity, planning IP allocation, and understanding subnetting for certifications.

How to Use the Subnet Calculator (CIDR)

Use the Subnet Calculator (CIDR) to subnet masks, network addresses, broadcast addresses, usable host ranges, and IP address allocations from IP addresses and CIDR notation (/24, /16, etc.) for comprehensive network planning. Features IPv4 and IPv6 support, binary conversions, subnet splitting, supernetting analysis, and network capacity planning. Essential for network administrators, IT professionals, system engineers, and cybersecurity specialists designing networks, troubleshooting connectivity, planning IP allocation, and understanding subnetting for certifications.. Enter your values to get accurate, instant results tailored to your situation.

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Subnet & CIDR Guide

Master IP address planning

Expert Tips

CIDR Numbers Show Network Size: The number after the slash indicates how large your network is. Smaller numbers mean bigger networks, larger numbers mean smaller, more focused segments.
Plan for Growth: Networks grow faster than expected. Choose a size that gives you room to add devices without having to reorganize everything later.
Not All Addresses Are Usable: Every subnet reserves the first and last addresses for special purposes. The actual number of devices you can connect is always slightly less than the total.
Use Private Address Ranges: Internal networks should use designated private IP ranges. These addresses work within your network but don't conflict with internet addresses.
Separate Networks for Security: Dividing your network into segments (servers, workstations, IoT devices) improves security. If one segment is compromised, others remain protected.

Essential Fundamentals — Understanding subnets

How Subnetting Works

The Slash Notation: CIDR notation like /24 or /28 tells you how the address space is divided. Think of it as defining the size of your network neighborhood.
Subnet Masks: The mask determines which part of an address identifies the network and which part identifies individual devices. Devices on the same subnet can communicate directly.
Usable Address Count: You can't use every address for devices—some are reserved for network management. Our calculator shows you exactly how many devices you can actually connect.

Choosing the Right Size

Home and Small Office: Standard home network sizes give you plenty of addresses for computers, phones, smart devices, and guests.
Business Networks: Larger organizations use different sizes for different purposes—bigger subnets for general use, smaller ones for specialized equipment.

Advanced Strategies — Network design patterns

Smart Network Planning

Group by Purpose: Keep similar devices together on their own subnets. This makes management easier and improves security through natural separation.
Allow for Expansion: When planning address allocations, leave room for future subnets. A little planning now saves major headaches later.

Frequently Asked Questions

What is CIDR notation?: CIDR (Classless Inter-Domain Routing) notation like /24 represents the number of bits used for the network portion of an IP address. A /24 means the first 24 bits are the network, leaving 8 bits (256 addresses) for hosts.
What's the difference between network and broadcast address?: The network address is the first address in a subnet (all host bits are 0) and identifies the network itself. The broadcast address is the last address (all host bits are 1) and is used to send messages to all hosts on the subnet.
Why can't I use the network and broadcast addresses for hosts?: The network address identifies the subnet itself, and the broadcast address is reserved for sending data to all hosts. That's why usable hosts = total hosts - 2 (except for /31 and /32 subnets which have special uses).
What is a wildcard mask?: A wildcard mask is the inverse of a subnet mask. It's used in access control lists (ACLs) and routing protocols like OSPF. Where a subnet mask has 1s, the wildcard has 0s, and vice versa.
What are private IP address ranges?: Private IP ranges are: 10.0.0.0/8 (Class A), 172.16.0.0/12 (Class B), and 192.168.0.0/16 (Class C). These can be used on internal networks and aren't routable on the public internet.