def _create_ip(subnet, index):
return '<STR_LIT:.>'.join(subnet.split('<STR_LIT:.>')[:<NUM_LIT:3>] + [str(index)])<EOL>
Given a subnet or an ip and an index returns the ip with that lower index
from the subnet (255.255.255.0 mask only subnets)

Args:
    subnet (str): Strign containing the three first elements of the decimal
        representation of a subnet (X.Y.Z) or a full ip (X.Y.Z.A)
    index (int or str): Last element of a decimal ip representation, for
        example, 123 for the ip 1.2.3.123

Returns:
    str: The dotted decimal representation of the ip