As developers and cloud architects, we are constantly planning VPCs, slicing up subnets for Kubernetes, and trying to avoid IP overlap across multi-region deployments. And like most people, I used to just Google "subnet calculator" and use whatever popped up first.
But I realized a massive security flaw in this workflow: most online subnet calculators process your inputs on their remote servers.
Whenever we type our internal IP schemas, CIDR blocks, or exact network topologies into these tools, we are essentially broadcasting our corporate network architecture to a third-party server. For a profession that obsesses over IAM roles, zero-trust networks, and private endpoints, this felt like a glaring blind spot.
Network planning should be secure, fast, and entirely private. So, I built DevSubnet.
What is DevSubnet?
DevSubnet is a free, 100% client-side IP subnet and CIDR calculator. There is zero server-side processing, no database logging your inputs, and no telemetry tracking your IP architectures. Everything executes locally in your browser via JavaScript.
While building it, I also wanted to solve the real-world headaches I face when provisioning infrastructure, going beyond the basic RFC 1918 math.
Key Features Built for Modern DevOps:
- Cloud Provider Offsets: Standard calculators assume you lose 2 IPs per subnet (Network and Broadcast). But if you deploy in the cloud, you know that AWS reserves 5 IPs, Azure reserves 5 IPs, and GCP reserves 4. DevSubnet automatically adjusts your usable host counts based on your selected cloud provider.
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Infrastructure as Code (IaC) Export: Once you have your CIDR blocks sliced correctly, you can instantly export configuration syntax for Terraform (
cidrsubnet()), AWS CloudFormation, Azure Bicep, Ansible, and Linuxiproute2. -
Interactive Visual Splitter: Slicing a
/16into multiple/24s for different availability zones? The recursive visual splitter lets you build out your architecture tree visually. - Kubernetes CNI Sizing: Quickly size Pod and Service CIDR blocks for Cilium, Calico, and AWS VPC CNI to prevent pod scheduling failures down the line.
Try It Out
You can use the tool completely free here: DevSubnet.com
Whether you are studying for a networking certification, writing Terraform modules, or architecting a multi-AZ cloud environment, I would love to hear your thoughts.
What is your current workflow for planning IP blocks? Are there any specific IaC exports or cloud provider quirks you would like to see added? Drop your feedback in the comments!
Top comments (1)
Thanks for reading! If there are specific cloud provider quirks (like OCI or Alibaba Cloud) or IaC templates (Pulumi, CDK) you'd like added to DevSubnet, let me know below