Subnet / CIDR Calculator

Calculate IP subnet mask, network address, broadcast address, IP range, wildcard mask, and usable host count from IP and CIDR prefix.

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主な特徴とプライバシー保証

  • ✓ 100%ブラウザ内完結: データは端末外に出ず、外部サーバーに送信されることはありません。
  • ✓ リアルタイム高速出力: ネットワーク遅延ゼロ、入力と同時に即時反映・高速コピー。
  • ✓ 永久無料＆制限なし: 会員登録不要、課金なし、1日の利用制限も一切ありません。
  • ✓ 標準規格準拠: RFC、ISO、W3Cウェブ標準仕様に厳密に準拠して設計されています。

IP Subnet Mask & Network Range Calculator

Calculate IPv4 network boundaries, wildcard masks, and total usable hosts instantly. Works offline in your browser for DevOps, sysadmins, and network engineers.

技術仕様とアーキテクチャ

Execution Environment:
100% Client-Side Browser Sandbox
Data Privacy:
Zero Server Storage / No Tracking
Processing Speed:
Real-time local CPU execution
Cross-Platform:
Works on Windows, macOS, Linux, iOS & Android

Local Processing for Network Tools

This tool runs within your browser sandbox using modern Web APIs. Inputs are processed on your local device CPU, avoiding network latency and ensuring your data is never stored on external servers or accessible to third parties.

1

Provide Input

Enter, paste, or upload your data into the input field above.

2

Configure & Process

The tool immediately processes your input in real time according to your chosen settings.

3

Copy or Save

Use the Copy button to copy the output to your clipboard, or download the result to your device.

開発者メモ: All operations execute locally in your browser memory for maximum speed and data privacy.

主な利用シーン

  • Design VPC and subnet ranges in AWS, Google Cloud, or Azure
  • Calculate usable IP addresses for DHCP pools and router configuration
  • Verify wildcard masks for Cisco ACLs and firewall rules
  • Convert CIDR notation (/27, /28) to dotted decimal subnet masks (255.255.255.224)

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よくある質問

What is a CIDR notation?
CIDR (Classless Inter-Domain Routing) notation specifies an IP address and its associated network prefix length (e.g. /24). The prefix number indicates how many leading bits are used for the network ID.
How many usable hosts in a /24 subnet?
A /24 subnet provides 256 total IP addresses, of which 254 are usable for hosts (excluding the network address .0 and broadcast address .255).
What is the difference between Subnet Mask and Wildcard Mask?
A Subnet Mask uses 1s for the network portion (e.g. 255.255.255.0). A Wildcard Mask is the bitwise inverse (e.g. 0.0.0.255), commonly used in Cisco ACLs and OSPF routing.
Is my IP data sent to any server?
No — all subnet calculations are performed entirely in your browser using local JavaScript.