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Wildcard Mask Calculator

Enter a subnet mask to get its wildcard mask.

How to use

  1. Enter your values in the fields above.
  2. Press Calculate to see your result instantly.
  3. Use the Share button to copy a link to your result.

About this calculator

This calculator converts a standard dotted-decimal subnet mask into its wildcard mask — the exact inverse, computed octet by octet as 255 − mask octet (so a /24 mask of 255.255.255.0 becomes the wildcard 0.0.0.255).

Wildcard masks flip the logic of a normal netmask: a 0 bit means "must match" and a 1 bit means "don't care," the opposite of a subnet mask. Network engineers use them specifically because Cisco IOS access control lists (ACLs) and the OSPF routing protocol require addresses to be specified in wildcard form rather than standard mask form.

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