Wildcard Mask Calculator

Convert a network and prefix length into its subnet mask and wildcard mask (the inverted mask ACLs and OSPF network statements use), plus a ready-to-paste ACL line.

Provided as-is, with no warranty of any kind. This runs entirely in your browser as a convenience tool, not a certified reference — always double-check results before relying on them for anything important, especially production changes. See the full disclaimer.