A wildcard mask is similar to a subnet mask but in the reverse.
An IPv4 ACE uses a 32-bit wildcard mask to determine which bits of the address to examine for a match. Wildcard masks are also used by the Open Shortest Path First (OSPF) routing protocol.
A wildcard mask is similar to a subnet mask in that it uses the ANDing process to identify which bits in an IPv4 address to match. However, a wildcard mask and a subnet mask differ in the way they match binary 1s and 0s. Unlike with a subnet mask, in which binary 1 is equal to a match, and binary 0 is not a match, with a wildcard mask, the reverse is true.
Wildcard masks use the following rules to match binary 1s and 0s:
