| CIDR Notation | - |
| Netmask | - |
| Wildcard Mask (ACL) | - |
| Network Address | - |
| Broadcast Address | - |
| Usable Host Range | - |
| Total Usable Hosts | - |
Subnetting and Zero Trust Micro-segmentation
Calculating precise CIDR blocks is essential when isolating critical network assets, defining cloud Security Groups (AWS VPC, Azure NSGs), and preventing lateral attack movement.
Wildcard Masks in Access Control Lists (ACLs)
A wildcard mask is the bitwise inverse of a subnet mask. Firewalls and Cisco IOS ACLs utilize wildcard masks to identify exact matching bits (0s) versus variable bits (1s).
About the Subnet Calculator
The IPv4 Subnet Calculator is a network engineering utility designed to assist security analysts, system administrators, and penetration testers in rapidly translating IP ranges into CIDR notation, identifying broadcast addresses, and determining usable host ranges.
Methodology & Use Cases
- Firewall Configuration: Accurately calculate CIDR blocks when defining strict ingress/egress rules in perimeter firewalls.
- Threat Hunting: Map out the exact boundaries of a compromised subnet to isolate lateral movement.
- Privacy Notice: This tool operates 100% locally within your browser using JavaScript. No IP addresses or subnet topologies are logged, stored, or transmitted to any remote servers.
Last Updated: September 2026. Note: This tool currently supports IPv4 only.