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Note Like an IP address, the mask is a 32-bit value. To set a range of addresses, each bit in the mask is compared to the corresponding bit in the IP address. Where the value in the mask is 1, the corresponding bit in the IP address is included in the list. Where the value in the mask is 0, any value is acceptable. For example, in decimal notation, if the IP address in the list is 134.123.123.20 and the mask is 255.255.255.0, all IP addresses from 134.123.123.0 to 134.123.123.255 are included in the list. If the mask is 255.255.255.128, all IP addresses from 134.123.123.0 to 134.123.123.127 are included in the list. If you specify an invalid mask, then the IP address is ignored. If you leave the IP mask blank, then it is considered to be 255.255.255.255.
Your ability to make changes to the registry by using Registry Editor depends on your access permissions. Incorrectly editing the registry can severely damage your system. Before making changes to the registry, back up any valued data on the computer.