CIDR Calculator — Free Online CIDR Range Calculator
Calculate IP ranges, host counts, and network details from CIDR notation — list all IPs in small ranges.
Frequently Asked Questions
CIDR Notation: Modern IP Address Range Management
CIDR replaced the original class-based IP addressing system (Class A, B, C) in 1993 to solve the rapid depletion of IPv4 addresses. By allowing arbitrary prefix lengths instead of fixed 8/16/24-bit boundaries, CIDR enabled more efficient allocation of IP address space to organizations based on their actual needs.
Today, CIDR is foundational to cloud networking. AWS Security Groups, Azure NSGs, GCP firewall rules, and Kubernetes network policies all use CIDR blocks to define network access rules. Understanding how to read and calculate CIDR ranges is essential for any infrastructure or DevOps role.
Common CIDR use cases: VPC subnet sizing (/20 for 4096 addresses), firewall rule specificity (/32 for single-IP rules), BGP route aggregation (combining multiple smaller routes into a single larger prefix), and Kubernetes pod/service CIDR allocation (/16 providing 65536 pod addresses).