Network Analysis Using Wireshark 2 Cookbook - Second Edition

How it works...

There are two modes of FTP: active and passive. In active mode, the server opens another connection to the client, while in passive mode, it is the client that opens the second connection to the server. Let's see how it works.

In passive mode, the operations are as shown in the following diagram:

Figure 12.4: FTP passive mode steps

These are described here:

1. The client opens a control connection from a random port P (1024 in the example) to server port 21
2. The server answers back from port 21 to the client port 1024
3. Now, the client opens a data connection from the port P+1 (1025 in the example) to a data port that the server ...