Why are only 254 addresses usable in a /24 network?

Every subnet reserves its first address as the network address and its last address as the broadcast address, so they can't be assigned to individual hosts. A /24 has 256 total addresses, minus those two reserved ones, leaving 254 usable.

What's a /31 or /32 used for?

A /32 identifies a single host with no room for a network or broadcast address — often used for loopback addresses or very specific routing rules. A /31 is a special case (defined in RFC 3021) used for point-to-point links between exactly two devices, where both addresses are usable since there's no broadcast address reserved.

Hostperl DNS Tools

Subnet Calculator

Enter a CIDR block to instantly calculate the network address, broadcast address, usable host range, and subnet mask.

Subnetting splits a network into smaller segments for routing, security, or organizational purposes. This calculator breaks down any CIDR block into its network, broadcast, and usable host range instantly.

Frequently asked questions

The number after the slash is the prefix length — how many bits of the 32-bit IPv4 address are fixed as the network portion. A /24 means the first 24 bits are the network, leaving 8 bits (256 addresses, 254 usable) for hosts. A smaller number after the slash means a larger network.