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A wildcard mask is a sequence of binary bits which helps in streamlining the routing of packets within a subnet of a network. It is shown over the subnet number, providing the router information about which parts of the subnet number to focus on. The use of the wildcard mark helps the router to only focus on the digits chosen by the mask rather than on the entire IP address. Wildcard masks are normally used to specify which IP addresses can be allowed or denied in the access control lists and with router protocols like the Open Shortest Path First.
A wildcard mask is similar to a subnet mask in bit length, as it is 32 bits long. However, it acts as an inverted subnet. Any wildcard bit pattern is capable of being masked for verification. In a network, the subnet number performs the task of helping a routing a packet to its final destination, once it has reached the main gateway. A binary zero over a specific digit in the subnet number requests a focus on the digit, whereas a binary one over a specific digit in the subnet number signals to ignore the specific digit. With wildcard masks, the zero bits specify the corresponding bit position must match the same bit position in the IP address, whereas the one bits specify that the corresponding bit position need not match the bit position in the IP address.
Wildcard masks help in specifying the range of network addresses to be used. They are largely used in circumstances where subnet masks cannot be used, such as when two affected hosts are under different subnets where the wildcard mask can be used to group them together.