IP サブネット計算機
サブネット、CIDR、ネットワーク範囲を計算
Network Address
192.168.1.0
Broadcast Address
192.168.1.255
Subnet Mask
255.255.255.0
Wildcard Mask
0.0.0.255
First Host
192.168.1.1
Last Host
192.168.1.254
Total Hosts
256
Usable Hosts
254
IP Class
C
Binary Representation
11000000.10101000.00000001.00000000
| CIDR | Subnet Mask | Usable Hosts |
|---|---|---|
| /8 | 255.0.0.0 | 16,777,214 |
| /16 | 255.255.0.0 | 65,534 |
| /24 | 255.255.255.0 | 254 |
| /25 | 255.255.255.128 | 126 |
| /26 | 255.255.255.192 | 62 |
| /27 | 255.255.255.224 | 30 |
| /28 | 255.255.255.240 | 14 |
| /29 | 255.255.255.248 | 6 |
| /30 | 255.255.255.252 | 2 |
次に進む
関連する次のアクションでワークフローを続けます。
Privacy & Trust
Client-side networking math
Address calculations happen in the browser, so private network planning details stay local while you test ranges and CIDR ideas.
CIDR controls scale
Moving from `/24` to `/23` doubles the address space, while moving to `/25` halves it. Small prefix changes have large capacity effects.
Review special ranges
Subnet math is correct for private, public, and multicast addresses alike, but operational policies still differ across RFC1918, loopback, and public networks.
Export subnet summary
Copy the current subnet calculation or download it as a plain-text snapshot.
使い方
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入力フィールドに数値やパラメータを入力します。
即座に結果を取得
入力するとすぐに結果が更新されます — 送信ボタンは不要です。
コピーまたは保存
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このツールを使う理由
完全無料
隠れたコストもプレミアムプランもありません — すべての機能が無料です。
インストール不要
すべてブラウザで実行されます。ソフトウェアのダウンロードやインストールは不要です。
プライベート＆安全
データはデバイスの外に出ることはありません。サーバーにアップロードされることはありません。
モバイル対応
完全レスポンシブ対応 — スマートフォン、タブレット、デスクトップで利用できます。
IP Subnetting: Network Design and Address Planning
Key Takeaways
- Subnetting divides large IP networks into smaller, manageable segments — improving security, performance, and address utilization.
- CIDR notation (/24, /16, etc.) defines the network prefix length, determining how many hosts each subnet can accommodate.
- All subnet calculations are performed in your browser — your network architecture data stays private.
IP subnetting is a fundamental networking skill that enables efficient use of IP address space and logical network segmentation. Whether you are designing a corporate network, planning cloud VPC configurations, or troubleshooting connectivity issues, understanding subnet masks, CIDR notation, and address ranges is essential for every network engineer and cloud architect.
A /24 subnet provides 254 usable host addresses, while a /16 provides 65,534 — choosing correctly prevents address exhaustion.
Capacity Planning
Key Concepts
CIDR Notation
Classless Inter-Domain Routing (CIDR) notation like 192.168.1.0/24 specifies the network prefix length. The /24 means the first 24 bits are the network portion, leaving 8 bits (256 addresses) for hosts.
Subnet Mask
A subnet mask (e.g., 255.255.255.0 for /24) determines which bits of an IP address identify the network and which identify the host. ANDing an IP with its mask gives the network address.
Network, Broadcast, and Usable Addresses
Every subnet has a network address (first, all host bits 0), broadcast address (last, all host bits 1), and usable range (everything between). A /24 has 256 total addresses but only 254 usable.
VLSM — Variable Length Subnet Masking
VLSM allows different subnets within the same network to have different prefix lengths. This enables efficient address allocation — a /28 (14 hosts) for a small office and /22 (1022 hosts) for a data center.
Pro Tips
Always plan for growth — if you need 50 hosts now, use a /25 (126 hosts) or /24 (254 hosts) rather than a /26 (62 hosts).
Use private address ranges (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16) for internal networks to conserve public IPv4 addresses.
In cloud environments (AWS VPC, Azure VNet), remember that some addresses are reserved by the provider — typically the first 4 and last 1.
Document your subnet allocation plan — without documentation, overlapping subnets and routing conflicts are inevitable as networks grow.
All subnet calculations are performed entirely in your browser. Your network addressing information, which may reveal infrastructure details, is never transmitted to any server.