CIDR Subnet Calculator は何をしますか？
CIDR Subnet Calculator はブラウザ上でデータを調査するツールで、結果と制限を明確に示します。 検証済みの機能： CIDR parsing, Network and broadcast, Usable host range, Local unsigned arithmetic.
The prefix controls block size and host semantics
Use broader prefixes for larger address blocks and narrower prefixes for smaller ones. Confirm routing and platform policy for /31 and /32 networks rather than applying the ordinary two-address reservation mechanically.
使い方
- Enter an IPv4 address and prefix in address/CIDR form, such as 192.168.1.42/24.
- Select Calculate subnet.
- Copy the mask, wildcard, network, broadcast, usable range, and address counts into the network plan.
実際の入出力例
Calculate a /24 containing one host address
入力
192.168.1.42/24出力
Subnet mask: 255.255.255.0
Network: 192.168.1.0
Broadcast: 192.168.1.255
Usable range: 192.168.1.1–192.168.1.254
Usable hosts: 254A /24 leaves eight host bits, so the block contains 256 addresses under traditional subnet semantics.
一般的なエラーと対処
| 症状 | 原因 | 対処 |
|---|---|---|
| The page asks for IPv4/CIDR format. | The prefix is missing, the address has the wrong number of octets, or an octet is outside 0–255. | Use four decimal octets followed by /0 through /32. |
| /31 or /32 host counts look different from total minus two. | Point-to-point /31 and single-host /32 prefixes do not use the traditional network-and-broadcast reservation rule. | Apply RFC 3021 semantics for /31 and treat /32 as one host route. |
Important behavior of Subnet Calculator
このツール固有の制限： /31 and /32 networks follow point-to-point and single-host counting rather than the traditional two-address reservation.
標準と実装の参考資料
- RFC 4632 — Classless Inter-domain Routing (opens in a new tab)Documents IPv4 CIDR prefixes and address aggregation.
- RFC 3021 — 31-Bit Prefixes on IPv4 Point-to-Point Links (opens in a new tab)Defines the two usable-address behavior of /31 links.
Subnet Calculator — FAQ
Does the Subnet Calculator upload my input?
No. Processing runs in the current browser tab, and the page does not send tool input to a KitLumi processing endpoint.
What input does the Subnet Calculator accept?
It accepts an IPv4 address followed by a prefix from /0 to /32. The workspace checks the input and reports malformed or unsupported values before it produces a result.
What does the Subnet Calculator produce?
It produces mask, wildcard, network, broadcast, usable range, and address counts. Copy and download controls appear when the output format supports them.
What limitation should I know?
/31 and /32 networks follow point-to-point and single-host counting rather than the traditional two-address reservation.
更新内容
実質的な更新： Subnet Calculator: Added CIDR parsing, Network and broadcast, Usable host range, Local unsigned arithmetic, responsive controls, explicit runtime disclosure, and task-specific examples and limitations.