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

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: 2026-09-22 · Reviewed by Nham Vu