子網路計算工具

根據任意IPv4 CIDR計算網路位址、廣播位址、主機範圍以及主機數量。

如何使用本工具

1
Type an IPv4 address with a prefix length into the box, for example 192.168.1.0/24. The field is pre-filled with that example to start.
2
Read the results table as you type. The network and broadcast addresses, dotted-decimal subnet mask, first and last usable host, usable host count, and total address count appear immediately.
3
Adjust the prefix length (the number after the slash) to widen or narrow the subnet and watch the host counts change.
4
If you see an Invalid CIDR or Invalid IP message, fix the input. The prefix must be 0 to 32 and each of the four octets must be 0 to 255.

CIDR（無類別域間路由）表示法將子網路表達為IP/位數；例如，192.168.1.0/24表示前24位用於標識網路，剩餘8位（256個位址）用於主機。本工具會計算關於一個子網路你需要知道的一切：網路位址、廣播位址、可用主機範圍以及位址總數。

Sizing a subnet for an office VLAN by checking how many usable hosts a /26 or /25 provides before you assign it.
Finding the network and broadcast addresses you must exclude when configuring a static DHCP address pool.
Translating a CIDR prefix into the dotted-decimal subnet mask a router or firewall interface expects, for example /22 to 255.255.252.0.
Confirming the usable host range when writing an access-control list or firewall rule for a specific subnet.
Verifying that a /31 point-to-point link between two routers gives you exactly two usable addresses with no broadcast waste.
Teaching or studying subnetting for a networking course or a CCNA exam by experimenting with prefixes and seeing host math update live.

/31和/32是什麼？▼

/31是一個包含2個位址的子網路（點對點連結，無廣播）。/32則是單個主機。