FTP

We have introduced FTP previously, and we mentioned that it is a means of transferring files across different operating systems, and requires an FTP server and an FTP client. Recall that it uses port 20 for data and 21 for commands. There are two types of FTP mode in use:

• Active FTP
• Passive FTP (sometimes written PASV)

Let's discuss these one by one.

Active FTP

With active FTP, the client will open a random port and connect to the FTP server on port 21. For the purposes of this explanation, we will use port 2031 as the port opened on the FTP client. Therefore, command communication is taking place between port 2031 on the client and port 21 on the server. Once the initial connection has been made, the client opens...