CIDR Notation in 5 Minutes: The Only Networking Concept You Need

/24 means 256 addresses. /16 means 65,536. /32 means exactly one. The number after the slash is how many bits are locked in place. Once that clicks, subnetting stops being mysterious. I spent an embarrassing amount of time early in my career avoiding subnetting. I would copy VPC configurations from Stack Overflow and hope they worked. Then one afternoon I sat down and actually learned the binary math, and the whole thing took maybe fifteen minutes to understand permanently. What the slash number actually means An IPv4 address is 32 bits long. That is it. The number after the slash in CIDR notation tells you how many of those 32 bits define the network portion. The remaining bits define the host portion, which is where individual device addresses live. /24 means the first 24 bits are the network. That leaves 32 - 24 = 8 bits for hosts. 2^8 = 256 possible addresses. But two are reserved: the network address (all host bits set to 0) and the broadcast address (all host bits set to 1). So y