What is CIDR notation?

CIDR (Classless Inter-Domain Routing) notation expresses an IP address and its associated network prefix as a single string, for example 192.168.1.0/24. The number after the slash indicates how many leading bits are fixed in the network portion of the address.

How many usable hosts does a /24 subnet have?

A /24 subnet contains 256 total addresses. Two are reserved — the network address and the broadcast address — leaving 254 usable host addresses.

What is a wildcard mask?

A wildcard mask is the bitwise complement of the subnet mask. It is used in Cisco ACLs and OSPF configuration. For a /24 subnet (mask 255.255.255.0), the wildcard mask is 0.0.0.255.

What is the difference between a public and private IP address?

Private IP ranges (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16, and 127.0.0.0/8 for loopback) are reserved for internal use and are not routable on the public internet. All other IPv4 addresses are considered public.

IP Subnet Calculator

Name: IP Subnet Calculator
Availability: InStock
Author: Nham Vu

Enter an IPv4 address and CIDR prefix (or netmask) to get every subnet detail — plus split any subnet into smaller blocks.

IP Address

CIDR / Netmask

Binary View

IP address

Subnet mask

Wildcard

Network

Subnet Splitter

Divide this network into equal smaller subnets by specifying a longer prefix.

Target prefix length

#	Network	First Host	Last Host	Broadcast

Summary

Enter an IPv4 address and CIDR prefix (or netmask) to get every subnet detail — plus split any subnet into smaller blocks.

How it works

Enter an IPv4 address in the "IP Address" field, for example 192.168.1.0.
Enter the CIDR prefix such as /24, or a dotted-decimal netmask such as 255.255.255.0, in the second field.
Results appear immediately: network address, broadcast, host range, usable hosts, wildcard mask, binary views, class, and scope.
To split the subnet, scroll to the "Subnet Splitter" section, enter a target prefix length, and click Split.
Switch to the IPv6 tab to inspect a basic /64 or any IPv6 CIDR prefix.

Use cases

Planning IP address allocation for a new office network
Verifying firewall or ACL rules by checking host ranges and broadcast addresses
Learning subnetting for CompTIA Network+ or CCNA certification study

Frequently Asked Questions

Last updated: 2026-06-09 · Reviewed by Nham Vu