CIDR Calculator

Calculate CIDR notation, subnet masks, and IP ranges.

Input

IP Address

CIDR / Subnet Mask

Network Info

255.255.255.0

Netmask

254

Hosts

Network Address

192.168.1.0

Range

192.168.1.1 - 192.168.1.254

Broadcast

192.168.1.255

Overview

CIDR (Classless Inter-Domain Routing) notation specifies IP address ranges using a slash followed by prefix length (e.g., /24). Essential for network design, firewall rules, and IP allocation. Replaced old class-based system (A, B, C).

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Pro Tips

/24 = 256 addresses (254 usable); /32 = single IP.
Private ranges: 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16.
Subnet mask for /24 is 255.255.255.0.
Smaller prefix = more addresses; /16 > /24 > /32.

Fun Facts

"CIDR was introduced in 1993 to slow IPv4 exhaustion."
"/24 is most common for home and small business networks."
"IPv6 uses similar notation but with 128-bit addresses."
"AWS VPCs typically use /16 or /20 CIDR blocks."

Formula: Usable IPs = 2^(32-prefix) - 2 (excluding network and broadcast)

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