Subnet

A subnet is a technique for dividing a large network into smaller ones, using the subnet mask to separate the network number from the host number, improving address utilization and isolation.

Purpose

It partitions the address space into logical subnets, keeping broadcast domains and routing tables manageable.

Mechanism

The subnet mask's leading run of 1s marks the network bits. For example, 255.255.255.0 means the first 24 bits are the network number and the last 8 the host part (256 addresses, 254 usable). In CIDR notation this is 192.168.1.0/24. Subnetting balances host count against subnet count.

Use cases

VLANs and network isolation
IP address planning
Firewall segmentation
Cloud VPC subnets

Examples

Input
```
192.168.1.0/24
```
Output
```
256 addresses, 254 usable
```
Network and broadcast addresses are reserved

Common errors

A non-contiguous subnet mask (e.g., 255.255.0.255): Masks must be a contiguous leading run of 1s

Related terms

CIDR (Classless Inter-Domain Routing) expresses a network as IP/prefix length (e.g., 10.0.0.0/8), replacing IPv4 address classes with flexible network partitioning.

IPv4 is the 32-bit network addressing protocol, written in dotted decimal (e.g., 192.168.1.1), with roughly 4.3 billion addresses—now exhausted.

IPv6 is the 128-bit network addressing protocol, written in colon-separated hexadecimal (e.g., 2001:db8::1), offering about 3.4×10^38 addresses to solve IPv4 exhaustion.

Related tools

IP Address Info

Analyze IPv4/IPv6 addresses and CIDR subnets: class, private/multicast flags, binary/hex, reverse DNS, network/broadcast/hosts. Free, private, and 100% client-side.

Subnet Calculator

Subnet Calculator — pure client-side tool. Privacy-first, no server round-trip.

Subnet Divider — pure client-side tool. Privacy-first, no server round-trip.

Ip Range Check — pure client-side tool. Privacy-first, no server round-trip.

References