Wildcard mask calculator
Convert a prefix or subnet mask to the wildcard mask used in ACLs and OSPF.
Runs on your device · nothing is uploaded
What is a wildcard mask?
A wildcard mask is the opposite of a subnet mask: every 0 bit means "must match" and every 1 bit means "any value". Cisco access lists and OSPF network statements use them. The quick way to work one out is to subtract each octet of the subnet mask from 255.
| Prefix | Subnet mask | Wildcard |
|---|---|---|
| /24 | 255.255.255.0 | 0.0.0.255 |
| /27 | 255.255.255.224 | 0.0.0.31 |
| /30 | 255.255.255.252 | 0.0.0.3 |