IPv4 wildcard mask
Convert a subnet mask to a wildcard mask (and back) in your browser. Nothing is uploaded.
IPv4 only. Calculate in this tab.
How to use the IPv4 wildcard mask
- Paste a dotted mask such as 255.255.255.0, or a wildcard such as 0.0.0.255.
- Click Calculate.
- Copy the pair plus the prefix length.
Mask vs wildcard
A contiguous mask is 1-bits then 0-bits. The wildcard is the bitwise inverse, which Cisco ACLs and some OSPF network statements still use. A value that is already all zeros then ones is treated as a wildcard and inverted to a mask.
Nothing is uploaded
Conversion is local.
IPv4 wildcard mask FAQ
Non-contiguous masks?
This page rejects holes in the 1-bits. Unusual ACL wildcards that skip bits are out of scope.
Need hosts too?
Use the CIDR calculator with the same prefix.