🔀 Wildcard Mask Calculator
Convert a subnet mask to its wildcard mask, or a wildcard mask back to a subnet mask. Commonly needed for Cisco ACLs and OSPF network statements.
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Wildcard masks identify which bits must match and which bits can vary. A wildcard mask is not itself a subnet mask — it is the mask's bitwise inverse, used by ACLs and routing protocols to specify match criteria.
How It Works
A wildcard mask is the bitwise complement (inverse) of a subnet mask: every 1 bit becomes 0 and every 0 bit becomes 1. Where a subnet mask says "these bits must match to be in this network," a wildcard mask says "these bits are allowed to vary" — the convention used by Cisco access control lists and OSPF network statements.
Examples & Common Use Cases
- 255.255.255.0 → wildcard 0.0.0.255 (matches any host in a /24).
- 255.255.255.240 → wildcard 0.0.0.15 (a /28).
- In a Cisco ACL:
access-list 10 permit 192.168.1.0 0.0.0.255uses a wildcard mask, not a subnet mask.