Wildcard Mask Calculator - Free ACL Utility
Calculate wildcard masks for ACLs and routing protocols.
Data Privacy & Security
100% Local Processing. Your data never leaves your browser. All calculations are securely executed using client-side JavaScript.
How to Use Wildcard Mask Calculator
- Enter a standard Subnet Mask or select a CIDR notation from the input options.
- Execute the bitwise calculation by pressing the Enter key or Calculate button.
- Immediately copy the generated wildcard mask for your router configurations.
Tool Limitations & Specs
- Operates exclusively via DOM-level JavaScript without server validation.
- Inputs exceeding standard format lengths will be securely rejected.
- Does not interact with external DNS or ICMP systems.
- Requires HTML5 Canvas and modern browser capabilities.
Frequently Asked Questions
What is a wildcard mask?
A wildcard mask is a 32-bit value that acts as an inverse to a subnet mask. It tells a router which parts of an IP address must match a rule, and which parts can be ignored.
How is a wildcard mask calculated?
It is calculated by taking a standard subnet mask and inverting its binary bits. In decimal, you can subtract each octet of the subnet mask from 255.
Why are wildcard masks used in OSPF?
Routing protocols like OSPF use wildcard masks to define which specific interfaces should participate in the routing process without being restricted to classful network boundaries.
How do wildcard masks work in Access Control Lists (ACLs)?
In Cisco ACLs, a 0 in the wildcard mask means the corresponding IP bit must match exactly, while a 1 means the bit can be any value (wildcard).
What is the wildcard mask for a /24 subnet?
A /24 subnet mask is 255.255.255.0. Subtracting this from 255.255.255.255 gives you a wildcard mask of 0.0.0.255.
Can a wildcard mask be non-contiguous?
Yes! Unlike subnet masks, wildcard masks can have non-contiguous bits (e.g., 0.255.0.255) to match highly specific, disjointed IP patterns, though this is rarely used.
What does a wildcard mask of 0.0.0.0 mean?
A wildcard mask of 0.0.0.0 enforces an exact match for all 32 bits, meaning it targets one single specific host IP address.
Does this tool transmit my ACL rules?
Absolutely not. This calculator executes the bitwise inversion mathematics locally in your browser sandbox to ensure total security.