Wildcard Mask Calculator (Cisco ACL)
Convert a CIDR prefix into the wildcard mask used in Cisco ACLs and generate the example ACL line.
What the wildcard mask is
In Cisco ACLs you don't use the subnet mask but the wildcard, which is its inverse. Where the mask has 0, the wildcard has 255, and vice versa. A /24 (255.255.255.0) becomes the wildcard 0.0.0.255: the first three octets must match exactly and the last one is "don't care".
0 in the wildcard = must match. Bit 1 = ignore. That is why 0.0.0.255 means "check the whole /24 network".Usage example
The ACL line generated above permits the entire range of the given network. Swap permit for deny to block, and adjust the source/destination to match your policy.
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