Tính subnet CIDR

Phân tích dải CIDR, tính dải địa chỉ, chia nhỏ subnet và kiểm tra một IP có nằm trong mạng hay không.

Chạy cục bộ trên trình duyệt

// cidr block

Network address10.0.0.0

Broadcast address10.0.255.255

First usable10.0.0.1

Last usable10.0.255.254

Usable hosts65,534

Total addresses65,536

Subnet mask255.255.0.0

Wildcard mask0.0.255.255

Prefix length/16

// check if an IP is inside this network

// split /16 into smaller subnets

target /

#	Network	Range	Usable
0	10.0.0.0/18	10.0.0.1 - 10.0.63.254	16,382
1	10.0.64.0/18	10.0.64.1 - 10.0.127.254	16,382
2	10.0.128.0/18	10.0.128.1 - 10.0.191.254	16,382
3	10.0.192.0/18	10.0.192.1 - 10.0.255.254	16,382

Cách hoạt động

How CIDR works

Prefix length

The number after the slash is the prefix length. It tells you how many bits of the address are the network portion. /24 means the first 24 bits are the network, leaving 8 bits (256 addresses) for hosts.

Usable vs total

Every normal subnet reserves the first address for the network identifier and the last for broadcast. Usable hosts = total addresses minus 2. Point-to-point links (/31) and host routes (/32) are the exceptions.

Common prefixes

/32: a single host (1 address)
/30: 4 addresses, 2 usable (point-to-point link)
/24: 256 addresses, 254 usable (classic LAN)
/16: 65,536 addresses (AWS VPC default)
/8: 16,777,216 addresses (one of the old class-A ranges)

Câu hỏi thường gặp

What does /24 mean in CIDR?

A /24 CIDR block has 24 bits of network prefix, leaving 8 bits for hosts. That gives 256 total addresses, of which 254 are usable (the first is the network address, the last is broadcast).

How many usable IP addresses does a /16 have?

A /16 has 2^16 = 65,536 total addresses. Subtracting the network and broadcast addresses leaves 65,534 usable host addresses. AWS VPCs commonly use /16 as the VPC CIDR.

Can I split a CIDR block into smaller subnets?

Yes. Use the subnet splitter on this page to divide a parent CIDR into equal-sized children. For example, a /16 can be split into 4 /18 subnets, 16 /20 subnets, and so on.

How do I check if an IP is inside a CIDR range?

Enter the CIDR block, then paste the IP into the checker. The tool bit-masks the IP with the subnet mask and compares it to the network address to confirm inclusion.

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Tính subnet CIDR

Cách hoạt động

How CIDR works

Prefix length

Usable vs total

Common prefixes

Câu hỏi thường gặp

Công cụ khác

Giải mã JWT

Mã hoá / giải mã Base64 và URL

Tạo UUID và secret