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IPv4 / IPv6 CIDR Subnet Calculator

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CIDR Subnet Calculator

Calculate IPv4/IPv6 CIDR subnets, broadcast addresses, usable hosts, and netmasks.
Last updated: July 7, 2026100% Client-Side & Private
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Ready: CIDR Subnet Calculator

Calculate IPv4/IPv6 CIDR subnets, broadcast addresses, usable hosts, and netmasks.

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About this Tool

Calculate IPv4/IPv6 CIDR subnets, broadcast addresses, usable host ranges, and binary netmasks in local memory.

Understanding CIDR Subnetting (RFC 4632)

Classless Inter-Domain Routing (CIDR) allocates IP addresses and routes internet traffic efficiently. A CIDR notation like 192.168.1.0/24 specifies both the IP network prefix and the number of fixed routing bits.

Subnet Calculations Explained

The calculator determines the network subnet address (bitwise AND of IP and mask), broadcast address (bitwise OR with inverted wildcard mask), first usable host, last usable host, total host capacity ($2^{32-\text{CIDR}}$), and binary representations.

Private vs Public Address Space (RFC 1918)

Automatically classifies IP ranges into Class A, B, C, Multicast, or Experimental, and identifies RFC 1918 private networking blocks (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16).

Privacy Guarantee

The IPv4 / IPv6 CIDR Subnet Calculator operates 100% locally in your web browser. Your inputs, configurations, and sensitive text payloads are processed entirely client-side using JavaScript and are never transmitted across the network or stored on any external servers.