Subnetting is a fundamental networking concept that helps to divide a larger network into smaller, more manageable subnetworks. Understanding subnetting is essential for controlling IP address allocation and improving network organization, whether you are working on home networks, enterprise systems, or data center configurations.
CIDR (Classless Inter-Domain Routing) is a method of allocating and routing IP packets. CIDR notation consists of two parts: an IP address, followed by a slash (/) and a number that represents how many bits are allocated for the network portion of the address.
CIDR to Subnet Mapping Table
Here’s a table that shows how many IP addresses are available for each subnet mask:
Subnet mask cheat sheet :
| CIDR | Total IPs | Usable IPs | Netmask |
| /16 | 65536 | 65534 | 255.255.0.0 |
| /17 | 32768 | 32766 | 255.255.128.0 |
| /18 | 16384 | 16382 | 255.255.192.0 |
| /19 | 8192 | 8190 | 255.255.224.0 |
| /20 | 4096 | 4094 | 255.255.240.0 |
| /21 | 2048 | 2046 | 255.255.248.0 |
| /22 | 1024 | 1022 | 255.255.252.0 |
| /23 | 512 | 510 | 255.255.254.0 |
| /24 | 256 | 254 | 255.255.255.0 |
| /25 | 128 | 126 | 255.255.255.128 |
| /26 | 64 | 62 | 255.255.255.192 |
| /27 | 32 | 30 | 255.255.255.224 |
| /28 | 16 | 14 | 255.255.255.240 |
| /29 | 8 | 6 | 255.255.255.248 |
| /30 | 4 | 2 | 255.255.255.252 |