public static function write_geolocation_data_to_db($geolocation_data, $source)
 {
     // create and check connection
     $link = CheckrouteDatabase::connect();
     // write all entries in AS list to database
     foreach ($geolocation_data as $geolocation_entry) {
         $stmt = mysqli_prepare($link, "INSERT INTO IPRange_belongs_to_Country (ip_from, ip_to, country_code, assigning_rir, assigning_date, source) VALUES (?, ?, ?, ?, ?, ?)");
         if ($stmt === false) {
             trigger_error('Error: Insert statement failed. ' . htmlspecialchars(mysqli_error($mysqli)), E_USER_ERROR);
         }
         $bind = mysqli_stmt_bind_param($stmt, "ssssss", $geolocation_entry['ip_from'], $geolocation_entry['ip_to'], $geolocation_entry['country'], $geolocation_entry['assigning_rir'], $geolocation_entry['assigning_date'], $source);
         if ($bind === false) {
             trigger_error('Error: Bind of parameters failed. ', E_USER_ERROR);
         }
         $exec = mysqli_stmt_execute($stmt);
         if ($exec === false) {
             print_r($geolocation_entry);
             trigger_error('Error: execution of statement failed. ' . htmlspecialchars(mysqli_stmt_error($stmt)), E_USER_ERROR);
         }
     }
     // close database connection
     CheckrouteDatabase::close($link);
 }