Wildcard Mask Calculator
This page converts IPv4 subnet masks and wildcard masks without changing the existing form or result cards. The added content explains the operational meaning: wildcard masks are most often used in ACL and routing syntax where host bits are written as match-any values.
Inputs explained
Enter either a standard subnet mask such as 255.255.255.0 or a wildcard mask such as 0.0.0.255. Use the matching conversion button for the direction you need.
How it works
The math is straightforward. A wildcard mask is the inverse of the subnet mask, calculated by subtracting each octet from 255. Converting back simply inverts the same values again.
Wildcard Mask Calculator
Mask ↔ WildcardResult
Step-by-Step Example
Convert 255.255.255.0 to wildcard notation by subtracting each octet from 255. The result is 0.0.0.255. Reversing the process gives you the original subnet mask again.
Use Cases
Use wildcard conversion when building ACL rules, route filters, or training materials for platforms that expect inverse mask syntax.
Assumptions and limitations
The output is exact mathematical inversion. It does not decide whether your target platform expects a host mask, wildcard mask, or CIDR prefix in a specific command.
Frequently Asked Questions
What is a wildcard mask?
A wildcard mask is the inverse of an IPv4 subnet mask and is commonly used in ACL and routing configurations.
How do I convert a subnet mask to a wildcard mask?
Subtract each subnet mask octet from 255. For example, 255.255.255.0 becomes 0.0.0.255.
Can I convert in both directions?
Yes. This page converts subnet masks to wildcard masks and wildcard masks back to subnet masks.
When is this useful?
It is useful when writing ACL entries, route filters, and other network policies that expect wildcard notation.
Does wildcard notation replace CIDR planning?
No. It is a complementary notation used by some platforms. CIDR and subnet math still define the actual network boundary.
What limitations apply to the output?
The output is exact mask inversion. It does not validate whether the resulting value matches the policy intent of a specific ACL rule.
Sources & References
Related Tools
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