JWT Decoder
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Open toolCIDR Subnet Calculator
Parse CIDR blocks, compute ranges, split into smaller subnets, and check whether an IP lives inside a network.
Runs locally in your browser
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
// split /16 into smaller subnets
| # | 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 |
How it works
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)
Frequently asked questions
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.
Tools are ported from DevOps Daily under the MIT license.View original
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