The Wildcard Mask
The wildcard mask is typically the inverse of the subnet mask configured on that interface. In a subnet mask, binary 1 is equal to a match and binary 0 is not a match. In a wildcard mask, the reverse is true, as shown in here:
- Wildcard mask bit 0 – Matches the corresponding bit value in the address.
- Wildcard mask bit 1 – Ignores the corresponding bit value in the address.
The easiest method for calculating a wildcard mask is to subtract the network subnet mask from 255.255.255.255, as shown for /24 and /26 subnet masks in the figure.