What is CIDR notation?

CIDR (Classless Inter-Domain Routing) notation expresses an IP address and its associated network mask as a single value. For example, 192.168.1.0/24 means the first 24 bits are the network address (192.168.1) and the last 8 bits identify hosts (0-255). /24 corresponds to subnet mask 255.255.255.0.

How many hosts does a /24 subnet have?

A /24 subnet has 256 total addresses. Subtracting the network address and broadcast address leaves 254 usable host addresses. Formula: 2^(32-prefix) - 2 = usable hosts. A /24 gives 2^8 - 2 = 254 hosts.

Subnet Calculator

Calculate network address, broadcast address, usable host range, subnet mask, and wildcard mask from any IPv4/CIDR.

subnet-calc.sh

IP Address / CIDR

Prefix Length

Examples:

All Subnets at this prefix

CIDR Reference Table

CIDR	Subnet Mask	Total Addresses	Usable Hosts

Frequently Asked Questions

CIDR (Classless Inter-Domain Routing) notation represents an IP address and its network mask as a single value: IP/prefix. The prefix length (e.g., /24) indicates how many bits are the network portion. 192.168.1.0/24 means the first 24 bits identify the network (192.168.1) and the last 8 bits identify hosts within it.

The network address is the first address in a subnet (all host bits = 0). It identifies the subnet itself and cannot be assigned to a host. The broadcast address is the last address (all host bits = 1) and is used to send packets to all hosts in the subnet simultaneously. Only the addresses between them (exclusive) are assignable to hosts.

/24 (Class C): 254 usable hosts, 256 total addresses. /16 (Class B): 65,534 usable hosts, 65,536 total. /8 (Class A): 16,777,214 usable hosts, 16,777,216 total. Formula: 2^(32-prefix) - 2 = usable hosts (subtract network and broadcast).

RFC 1918 defines three private IP ranges not routable on the public internet: 10.0.0.0/8 (Class A, 16.7M addresses), 172.16.0.0/12 (Class B, 1M addresses), and 192.168.0.0/16 (Class C, 65K addresses). These are used for local networks (home, office, data center) behind NAT.