Network

Wildcard Mask Calculator

Convert subnet masks into wildcard masks for ACL rules.

Last validated: 2026-02-14

Wildcard Mask Calculator converts subnet masks to wildcard masks for ACL and network policy use. It is useful in environments where control lists require wildcard notation rather than CIDR. The tool prevents common inverse-mask mistakes. Use it when preparing router and firewall access rules.

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Input Pattern

Enter values in the left panel, keep units explicit, run the calculation, then copy or share the result. Invalid fields are highlighted immediately.

Wildcard Mask Input

Result

Wildcard mask: 0.0.0.255

Mask bits: 11111111.11111111.11111111.00000000

Wildcard bits: 00000000.00000000.00000000.11111111

How to use this tool

Enter subnet mask or CIDR prefix.
Run conversion to generate wildcard mask output.
Apply result in ACL entries and validate against test traffic.

Worked Example

Auto-generated from the tool's current default or entered inputs.

Example Inputs

Subnet mask: 255.255.255.0
Wildcard mask: 0.0.0.255
Binary mask: 11111111.11111111.11111111.00000000
Binary wildcard: 00000000.00000000.00000000.11111111

Expected Outputs

Interpretation

Confirm unit consistency and operational constraints before applying this result in production or field conditions.

Scenario Compare (A vs B)

Use this to compare two input sets and quantify change in key outputs.

Formula References

IPv4/IPv6 addressing rules and common protocol arithmetic.
DNS/WHOIS/network calls depend on external resolvers and current network state.

Assumptions

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