ConfigGenerator

CIDR Calculator

Calculate IPv4/IPv6 subnets, network addresses, broadcasts, and generate complex subnet splits.

Subnet Splitting

Enter a valid CIDR block to see the visual subnet plan.

CIDR Subnet Planning

What is CIDR Subnet Planning?

A CIDR (Classless Inter-Domain Routing) Calculator is a network planning tool that computes IP address ranges, broadcast addresses, and subnet masks from a base CIDR block. It helps engineers partition a large network into smaller, isolated subnets.

How it Works

Enter your base network CIDR (like 10.0.0.0/16). The tool instantly calculates the usable IP range and subnet mask. You can then choose to 'split' this block into smaller subnets (e.g., splitting a /24 into four /26 subnets) to plan multi-tier architectures like public/private database zones.

Best Practices

  • Always leave buffer IPs. Do not allocate 100% of your VPC space on day one. Leave room for future subnet expansion.
  • Remember that cloud providers (AWS, Azure, GCP) reserve the first 4 and last 1 IP addresses in every subnet for routing and internal DNS. A /28 (16 IPs) only gives you 11 usable IPs in AWS.
  • Use easily recognizable boundaries when possible (like /24) for easier mental mapping of network zones.

    • Common Mistakes

  • Overlapping CIDR blocks. If you plan to connect two VPCs via VPC Peering or a Transit Gateway, their CIDR blocks must not overlap.
  • Using a /16 for a single subnet. This creates an overly large broadcast domain and wastes massive amounts of private address space.
  • Forgetting to align subnet splits to powers of 2, leading to invalid routing tables.