What does /24 mean in CIDR notation?

/24 means the first 24 bits are the network portion, leaving 8 bits for hosts. A /24 subnet contains 256 IP addresses (2^8) with 254 usable hosts (subtracting network and broadcast addresses). This is the most common subnet size for LANs.

What CIDR ranges should I use for AWS VPCs?

AWS recommends using RFC 1918 private ranges: 10.0.0.0/8, 172.16.0.0/12, or 192.168.0.0/16. A common pattern is a /16 VPC (65,536 IPs) divided into /24 subnets (256 IPs each) per availability zone. Avoid /28 or smaller for production as they quickly exhaust with ENIs.

How many hosts does a /28 subnet support?

A /28 subnet has 16 IP addresses (2^4) with 14 usable hosts after subtracting the network and broadcast addresses. This is commonly used for small isolated services, load balancer subnets, or VPN gateway subnets in AWS.

What is the difference between subnet mask and wildcard mask?

Subnet mask (e.g., 255.255.255.0) marks which bits are the network portion with 1s. Wildcard mask (e.g., 0.0.0.255) is the inverse — 0s mark network bits and 1s mark host bits. Wildcard masks are used in Cisco ACLs and OSPF configurations.

How do I split a /24 into smaller subnets?

To split a /24 (256 IPs) into smaller subnets: /25 gives 2 subnets of 128 IPs each, /26 gives 4 subnets of 64 IPs, /27 gives 8 subnets of 32 IPs, /28 gives 16 subnets of 16 IPs. Each additional bit doubles the number of subnets and halves the size.

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CIDR / Subnet Calculator

Calculate network address, broadcast, subnet mask, usable hosts, and IP range from any CIDR notation. Free online CIDR and subnet calculator for network engineers.

CIDR Notation

Network Address192.168.1.0

Broadcast Address192.168.1.255

Subnet Mask255.255.255.0

Wildcard Mask0.0.0.255

First Usable IP192.168.1.1

Last Usable IP192.168.1.254

Usable Hosts254

Prefix Length/24

About This Tool

Calculate all subnet details from any CIDR notation instantly. Enter an IP address with prefix length (e.g., 192.168.1.0/24) and immediately see the network address, broadcast address, subnet mask, wildcard mask, first and last usable IP, and total number of usable hosts. Essential for network engineers, DevOps teams, cloud architects, and anyone working with AWS VPCs, Kubernetes networking, or firewall rules.

How It Works

Enter a CIDR notation in the format IP/prefix — for example 192.168.1.0/24 or 10.0.0.0/16

Instantly see all subnet properties — network address, broadcast, subnet mask, wildcard, first and last usable IPs

Use the usable hosts count to verify if the subnet has enough capacity for your workload

Try common cloud CIDR ranges — /16 for VPC, /24 for subnets, /28 for small isolated services

Frequently Asked Questions

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