What is a Subnet?

A subnet divides a large IP network into smaller, logically separated segments. Through subnetting, network administrators can manage IP addresses more efficiently, segment network traffic, and improve security. Our subnet calculator helps you compute CIDR notations, convert subnet masks, and determine available host addresses.

Understanding CIDR Notation

CIDR (Classless Inter-Domain Routing) replaces the old network classes A, B, C and uses a suffix (e.g., /24) to indicate the number of network bits.

Common Subnet Masks:
/8 = 255.0.0.0 → 16,777,214 Hosts
/16 = 255.255.0.0 → 65,534 Hosts
/24 = 255.255.255.0 → 254 Hosts
/25 = 255.255.255.128 → 126 Hosts
/26 = 255.255.255.192 → 62 Hosts
/27 = 255.255.255.224 → 30 Hosts
/28 = 255.255.255.240 → 14 Hosts
/30 = 255.255.255.252 → 2 Hosts (Point-to-Point)

Key Calculations

Number of Hosts: 2^(32 - CIDR) - 2 (minus network and broadcast address)
Network Address: First address in subnet (all host bits = 0)
Broadcast Address: Last address in subnet (all host bits = 1)
Usable IPs: All addresses between network and broadcast

Frequently Asked Questions (FAQ)

Why do I always lose 2 IP addresses in a subnet?

The first address is the network address (identifies the subnet) and the last is the broadcast address (reaches all devices in the subnet). Neither can be assigned to a host.

What's the difference between /24 and 255.255.255.0?

Both mean the same thing. /24 is CIDR notation (24 network bits), 255.255.255.0 is the decimal subnet mask. CIDR is shorter and preferred in modern networking.

What are the private IP ranges?

RFC 1918 defines: 10.0.0.0/8 (16M addresses), 172.16.0.0/12 (1M addresses), 192.168.0.0/16 (65K addresses). These are used in internal networks.

When should I use VLSM (Variable Length Subnet Masking)?

VLSM is ideal when different subnets need different sizes. E.g., /30 for point-to-point links (2 hosts), /24 for user networks (254 hosts).

💡 Tip: For home networks, a /24 subnet (254 devices) is usually sufficient. Plan enterprise networks with growth in mind and divide by departments or functions (servers, WiFi, IoT) into separate subnets.