Free online CIDR and IP address range calculator - Subnet mask, network/broadcast address, pure client-side
CIDR（无类别域间路由）用IP地址加斜杠和前缀长度表示网络，如192.168.1.0/24表示前24位是网络位，后8位是主机位。前缀长度越小，网络越大：/24有256个地址，/16有65536个地址，/8有约1677万个地址。
网络地址是子网中第一个IP（主机位全0），用于标识网络本身。广播地址是子网中最后一个IP（主机位全1），用于向子网内所有主机发送广播。这两个地址不能分配给设备使用。
每个子网中，网络地址（第一个）和广播地址（最后一个）保留不能分配给主机，所以可用主机数=总地址数-2。例如/24子网有256个地址，可用主机254个。但/31子网只有2个地址，按RFC 3021两个都可用（点对点链路）。
No. IP Range Calculator is a web-based tool — just open it in your browser and start using it. No downloads, plugins, or extensions required.
Yes. IP Range Calculator is fully responsive and works on phones, tablets, and desktops. The interface adapts automatically to your screen size.
Absolutely. All processing happens locally in your browser. No data is sent to any server, so there's zero risk of data leaks. Your information stays completely under your control.
No. IP Range Calculator uses client-side processing — everything runs in your browser. Your data never leaves your device, and the tool works even without an internet connection.
Yes, IP Range Calculator is completely free to use. No registration or login required — all features are available immediately.
Some tools make real requests while others work locally. Check the tool description for details.
Calculations use JavaScript's floating-point arithmetic with up to 15 significant digits of precision. For most practical purposes, this is more than sufficient.