What is the difference between subnet mask and CIDR notation?

A subnet mask is a 32-bit number written in dotted decimal format (e.g., 255.255.255.0) that identifies the network portion of an IP address. CIDR notation is a more compact representation using a slash followed by the number of network bits (e.g., /24). Both represent the same information, but CIDR is more concise and widely used in modern networking, especially in cloud infrastructure.

How many usable IP addresses are in a /24 subnet?

A /24 subnet (255.255.255.0) contains 256 total IP addresses, but only 254 are usable for devices. The first address is reserved as the network address and the last address is reserved as the broadcast address. Therefore, you can assign IP addresses to 254 hosts in a /24 subnet.

Can I use this calculator for IPv6 addresses?

This calculator is specifically designed for IPv4 addresses and subnet calculations. IPv6 uses a different addressing scheme with 128-bit addresses and different notation. For IPv6 subnetting, you would need a dedicated IPv6 calculator that handles the expanded address space and hexadecimal notation.

What is the smallest subnet I can create?

The smallest practical subnet is a /30 (255.255.255.252), which provides only 4 IP addresses total: 2 usable addresses for devices and 2 reserved addresses (network and broadcast). This is commonly used for point-to-point links like router-to-router connections. A /31 exists for special use cases with only 2 addresses.

How do I choose the right subnet size for my network?

To choose the right subnet size, estimate the maximum number of devices you'll need, then add a buffer for future growth (typically 20-30%). Use this calculator to find a subnet mask that provides at least that many usable addresses. For example, if you need 50 devices, a /25 (126 usable addresses) would be appropriate. Always plan for expansion rather than creating subnets that are exactly full.

Subnet / IP Calculator

IP Address

Prefix (CIDR)/24

/0/8/16/24/32

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Subnet / IP Calculator

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