Máy tính Subnet / CIDR

(Tài liệu bằng tiếng Anh)

What it does

The Subnet / CIDR Calculator turns any IPv4 CIDR block - like 192.168.1.0/24 - into a full subnet breakdown: network address, broadcast address, first and last usable host, subnet mask, wildcard mask, host count, classful IP class, and whether the range is private (RFC 1918). It also splits a block into smaller subnets of any prefix you choose. Everything runs 100% client-side, so nothing leaves your browser.

How to use it

1. Type a CIDR block into the CIDR block field (e.g. 10.0.0.0/8), or hit Sample.
2. Read the result grid: network, broadcast, host range, mask, wildcard, host count, class, and private-range flag - each with its own Copy button.
3. To divide the block, enter a larger prefix under Split into smaller subnets and review the generated child subnets.
4. Copy share link encodes your CIDR and split prefix in the URL, so a teammate sees the exact view.

Examples

Home network

192.168.1.0/24 → Network 192.168.1.0, Broadcast 192.168.1.255, Hosts 254, Mask 255.255.255.0, Class C, Private: Yes.

Point-to-point link

10.0.0.0/31 → 2 usable hosts (first = 10.0.0.0, last = 10.0.0.1), used for router-to-router links.

Split a /24

192.168.1.0/24 split into /26 → 192.168.1.0/26, 192.168.1.64/26, 192.168.1.128/26, 192.168.1.192/26.

Good to know

• Host counts follow the standard rules: 2^(32−prefix) − 2 for /1-/30; /31 returns 2 (point-to-point, per RFC 3021); /32 returns 1 (single host).
• Private ranges detected: 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16 (RFC 1918).
• Normalization: a host IP like 192.168.1.5/24 is masked to its network 192.168.1.0/24 before splitting.
• Shareable: the CIDR and split prefix live in the URL (?cidr=…&split=…).
• Related tools: Data Unit Converter, Number Base Converter.