The value of the object tmnxLocUsrDbPppoeMaskPreStr specifies a substring that is stripped off the start of the incoming string before it is matched against the value configured in the corresponding object in the tmnxLocUsrDbPppoeTable. This string can only contain printable ASCII characters. Character '*' is a wildcard that matches any substring; it can be escaped by character '\'. At least one of the values of tmnxLocUsrDbPppoeMaskPreNum and tmnxLocUsrDbPppoeMaskPreStr must be equal to the default value.