Wildcard Mask Calculator
Convert a subnet mask or CIDR prefix into the inverse wildcard mask used in Cisco ACLs.
| CIDR | /24 | |
| Subnet mask | 255.255.255.0 | |
| Wildcard mask | 0.0.0.255 | |
| Wildcard (binary) | 00000000.00000000.00000000.11111111 |
Enter a CIDR prefix or dotted subnet mask and instantly get the inverse wildcard mask used in access control lists, along with its binary representation. All calculations run in your browser.
How to use
- Choose whether you're entering a CIDR prefix or a dotted subnet mask.
- Type the value, e.g. /24 or 255.255.255.0.
- Read off the resulting mask, wildcard mask, and binary breakdown, or copy any value.
Frequently asked questions
- What is a wildcard mask used for?
- Wildcard masks are the inverse of a subnet mask and are used in Cisco ACL and OSPF configuration to match address ranges.
- How is the wildcard mask calculated?
- It's the bitwise complement (inverse) of the subnet mask: each 1 bit becomes 0 and each 0 bit becomes 1.
- Can I enter a mask instead of a CIDR prefix?
- Yes, switch the input type to dotted subnet mask and enter something like 255.255.255.0.