How To use SCP to transfer files to a remote server on port 21

In this tutorial, we’ll discuss how to use the Secure Copy Protocol (SCP) to transfer files to a remote server on port 21. We’ll also delve into the potential security risks and best practices associated with this method.

Introduction to SCP

SCP stands for Secure Copy Protocol. It’s a network protocol that allows files to be transferred over a network securely. SCP uses SSH (Secure Shell) for data transfer and utilizes the same mechanisms for authentication, thereby ensuring the confidentiality and integrity of the data in transit.

Understanding Ports

In networking, a port is a communication endpoint. By default, SSH uses port 22, and SCP, being a part of SSH, also uses the same. Port 21, on the other hand, is typically used for FTP (File Transfer Protocol).

However, it’s crucial to note that using port 21 for SSH and SCP is not recommended due to potential confusion and security risks. It’s best to use the default port 22 or a different port that is not commonly used for other protocols.

Configuring SSH Server to Listen on Port 21

If you still want to proceed with using port 21 for SSH and SCP, you need to configure the SSH server on the remote server to listen on port 21. Here’s how you can do it:

Step 1: Check if the SSH server is running on the remote server by connecting to it using SSH on port 22:

ssh username@secondhost

Replace username with your username on the remote server, and secondhost with the hostname or IP address of the remote server.

Step 2: If the connection is successful, open the SSH server configuration file on the remote server using a text editor:

sudo nano /etc/ssh/sshd_config

Step 3: Look for the line that specifies the port number and change it to 21:

Port 21

Step 4: Save the changes and exit the text editor.

Step 5: Restart the SSH server for the changes to take effect:

sudo service ssh restart

Transferring Files using SCP on Port 21

Now that the SSH server on the remote server is configured to listen on port 21, you can use the following command to transfer the file using SCP:

scp -P 21 /home/direc/file.tar username@secondhost:/home/dir

Here’s what each part of the command does:

• scp is the command to initiate the Secure Copy Protocol.
• -P 21 specifies that SCP should use port 21 for the connection.
• /home/direc/file.tar is the path and filename of the file you want to transfer.
• username@secondhost:/home/dir is the destination for the file. Replace username with your username on the remote server, secondhost with the hostname or IP address of the remote server, and /home/dir with the directory where you want to place the file on the remote server.

Conclusion

While it’s technically possible to use SCP to transfer files to a remote server on port 21, it’s not recommended due to potential confusion and security risks. It’s best to use the default port 22 or a different port that is not commonly used for other protocols.

By understanding how SCP works and how to configure the SSH server to listen on a different port, you can ensure that your file transfers are secure and efficient. Always remember to follow best practices for network security to protect your data.