Wildcard Mask Calculator
Convert IPv4 CIDR prefixes and subnet masks into wildcard masks.
What is a wildcard mask?
A wildcard mask is the bitwise inverse of a subnet mask. Where a subnet mask marks the network portion with 1 bits, a wildcard mask marks it with 0 bits — and marks the host portion with 1 bits. For example, the subnet mask 255.255.255.0 has the wildcard mask 0.0.0.255. Each 0 bit means “must match” and each 1 bit means “can vary”.
Where are wildcard masks used?
Wildcard masks appear mainly in Cisco IOS configuration: in access control lists (ACLs) to match a block of addresses, and in OSPF network statements to select which interfaces participate in routing. Some other vendors use them too, but they are not universal — many systems express the same idea with a CIDR prefix instead.
Example
The network 192.168.1.0/24 has subnet mask 255.255.255.0. Its wildcard mask is 0.0.0.255: the first three octets must match exactly, while the last octet may be any value — matching every address from 192.168.1.0 to 192.168.1.255.
Common wildcard masks
| Prefix | Subnet Mask | Wildcard Mask |
|---|---|---|
| /8 | 255.0.0.0 | 0.255.255.255 |
| /16 | 255.255.0.0 | 0.0.255.255 |
| /24 | 255.255.255.0 | 0.0.0.255 |
| /30 | 255.255.255.252 | 0.0.0.3 |
| /32 | 255.255.255.255 | 0.0.0.0 |
Related Tools
- CIDR Overlap Detector
- CIDR Summarizer — Coming soon
- IP Range to CIDR — Coming soon
- VLSM Planner — Coming soon