Портом по умолчанию для FTP (протокола передачи файлов) является порт номер 21. Вот несколько методов с примерами кода для работы с FTP на различных языках программирования:

1. Python:

   import ftplib
   # Connect to FTP server
   ftp = ftplib.FTP("ftp.example.com")
   ftp.login("username", "password")
   # List files in the current directory
   files = ftp.nlst()
   print(files)
   # Download a file
   filename = "example.txt"
   with open(filename, "wb") as file:
   ftp.retrbinary("RETR " + filename, file.write)
   # Upload a file
   filename = "example.txt"
   with open(filename, "rb") as file:
   ftp.storbinary("STOR " + filename, file)
   # Disconnect from the FTP server
   ftp.quit()

2. Java:

   import org.apache.commons.net.ftp.FTP;
   import org.apache.commons.net.ftp.FTPClient;
   public class FTPExample {
   public static void main(String[] args) {
       FTPClient ftp = new FTPClient();
       try {
           // Connect to FTP server
           ftp.connect("ftp.example.com", 21);
           ftp.login("username", "password");
           // List files in the current directory
           String[] files = ftp.listNames();
           for (String file : files) {
               System.out.println(file);
           }
   // Download a file
           String filename = "example.txt";
           ftp.setFileType(FTP.BINARY_FILE_TYPE);
           ftp.retrieveFile(filename, new FileOutputStream(filename));
           // Upload a file
           filename = "example.txt";
           ftp.setFileType(FTP.BINARY_FILE_TYPE);
           ftp.storeFile(filename, new FileInputStream(filename));
           // Disconnect from the FTP server
           ftp.logout();
           ftp.disconnect();
       } catch (IOException e) {
           e.printStackTrace();
       }
   }
   }

3. C#:

   using System;
   using System.IO;
   using System.Net;
   class Program
   {
   static void Main(string[] args)
   {
       string server = "ftp://ftp.example.com";
       string username = "username";
       string password = "password";
       // List files in the current directory
       FtpWebRequest request = (FtpWebRequest)WebRequest.Create(server);
       request.Method = WebRequestMethods.Ftp.ListDirectory;
       request.Credentials = new NetworkCredential(username, password);
       FtpWebResponse response = (FtpWebResponse)request.GetResponse();
       StreamReader reader = new StreamReader(response.GetResponseStream());
       string line = reader.ReadLine();
       while (!string.IsNullOrEmpty(line))
       {
           Console.WriteLine(line);
           line = reader.ReadLine();
       }
       reader.Close();
       response.Close();
       // Download a file
       string filename = "example.txt";
       request = (FtpWebRequest)WebRequest.Create(server + "/" + filename);
       request.Method = WebRequestMethods.Ftp.DownloadFile;
       request.Credentials = new NetworkCredential(username, password);
       response = (FtpWebResponse)request.GetResponse();
       Stream stream = response.GetResponseStream();
       StreamReader fileStream = new StreamReader(stream);
       using (StreamWriter writer = new StreamWriter(filename))
       {
           writer.Write(fileStream.ReadToEnd());
       }
       fileStream.Close();
       response.Close();
       // Upload a file
       filename = "example.txt";
       request = (FtpWebRequest)WebRequest.Create(server + "/" + filename);
       request.Method = WebRequestMethods.Ftp.UploadFile;
       request.Credentials = new NetworkCredential(username, password);
       using (FileStream fileStream = new FileStream(filename, FileMode.Open))
       {
           byte[] buffer = new byte[1024];
           int bytesRead;
           Stream requestStream = request.GetRequestStream();
           while ((bytesRead = fileStream.Read(buffer, 0, buffer.Length)) > 0)
           {
               requestStream.Write(buffer, 0, bytesRead);
           }
           requestStream.Close();
       }
   // Disconnect from the FTP server
       Console.WriteLine("File uploaded!");
   }
   }