数学

Subnet Calculator

IP Subnet Calculator

IP Address

Prefix length (CIDR)

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是什么 Subnet Calculator?

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An IP subnet calculator finds network address, broadcast address, usable host range, wildcard mask, and number of hosts from an IP/CIDR input like 192.168.1.0/24.

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公式

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f(x)Network address = IP AND subnet mask; Host count = 2^(32−prefix)−2; CIDR = /24 means /24 prefix bits

变量说明

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符号	名称	单位	描述
IP	IP address	IPv4 dotted decimal	—
SM	Subnet mask	dotted decimal or /prefix	—
n	Number of usable hosts	—	—

如何 Subnet Calculator

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1CIDR /n: first n bits = network; remaining bits = host addresses
2Network address: all host bits set to 0
3Broadcast: all host bits set to 1
4Usable hosts = 2^(32−n) − 2

例题解析

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示例 1

已知:10.0.0.0/8

结果:Network: 10.0.0.0; Broadcast: 10.255.255.255; Hosts: 10.0.0.1–10.255.255.254 (16,777,214 hosts)

实际应用

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Network administration and planning

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IP addressing schemes

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VLAN and network segmentation

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Network security and access control

Common Subnet Sizes

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CIDR	Hosts usable	Subnet mask	Use case
/30	2	255.255.255.252	Point-to-point links
/29	6	255.255.255.248	Small office
/24	254	255.255.255.0	Standard LAN
/16	65,534	255.255.0.0	Large network
/8	16.7M	255.0.0.0	Class A network

常见问题

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What's a subnet mask?

Defines network portion of IP (mask 1s) and host portion (mask 0s). /24 = 255.255.255.0.

How many hosts in /24 subnet?

2^(32−24)−2 = 2^8−2 = 256−2 = 254 usable addresses (network & broadcast reserved).

What's CIDR notation?

/24 means first 24 bits are network. Shorthand for subnet mask. 192.168.1.0/24 is cleaner than /255.255.255.0.

参考资料

›Subnetting — Cisco

Mathematically verified

Reviewed October 2026

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