The Ultimate Developer Tool for Network Planning
Whether you are studying for your CCNA, designing an AWS Virtual Private Cloud (VPC), or just trying to figure out why two Docker containers cannot communicate, understanding subnetting is a critical skill for any modern software engineer or DevOps professional.
Our CIDR/Subnet Calculator removes the manual math from network design. By simply typing an IP address and a slash notation (like 10.0.0.0/16), you get an instant, accurate breakdown of the entire subnet space. And because this tool runs entirely locally in your browser using JavaScript, your proprietary internal network designs are never sent to a remote server.
How This Tool Works
- Enter an IP: Type any valid IPv4 or IPv6 address with a CIDR suffix (e.g., `/24`).
- Instant Calculation: The tool uses native bitwise math to calculate the binary network mask and apply it to your IP.
- Results: You instantly receive the Network Address, Broadcast Address, the range of Usable IPs, and the total number of hosts available in that block.
AWS VPC Sizing
Cloud providers like Amazon Web Services (AWS), Google Cloud (GCP), and Azure do not give you access to all IPs in a subnet. For instance, AWS explicitly reserves the first four IP addresses and the last IP address of every subnet for internal networking purposes (Network address, VPC Router, DNS server, future use, and Network Broadcast address).
This tool automatically calculates the AWS Usable IPs to prevent you from accidentally provisioning a subnet that is too small for your Kubernetes clusters (EKS) or EC2 auto-scaling groups. If you enter a `/32` or `/31`, the tool will explicitly warn you that it is too small for AWS.
IPv6 Support
As the world transitions to IPv6, network masks become incredibly difficult to calculate mentally due to the massive 128-bit address space. This tool fully supports IPv6 CIDR parsing, instantly calculating start and end addresses for blocks like 2001:db8::/32.
Common Use Cases
- AWS Cloud Architecture: Planning a 3-tier VPC architecture with public, private, and database subnets without overlapping CIDR blocks.
- Kubernetes CNI Planning: Determining the correct `podCIDR` size for a Calico or Flannel network overlay to ensure you do not run out of pod IP addresses.
- Firewall Rules: Finding the exact IP range to whitelist in a Security Group when a partner says "allow `192.168.100.0/22`".
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Frequently Asked Questions
- What is CIDR notation?
- CIDR (Classless Inter-Domain Routing) notation is a compact representation of an IP address and its associated routing prefix. The number after the slash (e.g., /24) represents the number of bits in the subnet mask.
- Why does AWS reserve 5 IP addresses per subnet?
- AWS reserves the first four and the last IP address in every subnet for infrastructure purposes: the Network address, the VPC router, the Amazon-provided DNS server, a reserved IP for future use, and the Broadcast address.
- What is the difference between Network and Broadcast addresses?
- The Network address is the very first IP in a subnet and is used to identify the network itself. The Broadcast address is the very last IP and is used to send messages to all hosts on that specific network.
- Does this calculator support IPv6?
- Yes, this tool fully supports IPv6. If you enter an IPv6 address with a CIDR notation (like 2001:db8::/32), it will calculate the massive 128-bit address space to find your start and end ranges.