FTP Passive Mode Data Channel Ports
Question
Which port or ports are used for the FTP data channel in passive mode?
Answers
Explanations
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A. B. C. D. E.A.
When a client initiates an FTP session with a server, there are two types of connections that are established: control connection and data connection. The control connection is used for sending commands and responses between the client and server, while the data connection is used for transferring the actual file data.
In passive mode, the client sends a PASV (passive) command to the server, which responds with an IP address and port number for the client to use for the data connection. The client then initiates the data connection to the specified IP address and port number.
Answer A is incorrect because while the ports used for the data channel are random, they are not completely random. The server specifies the port range to use for the data channel.
Answer B is incorrect because TCP port 21 is used for the control connection, not the data connection.
Answer C is incorrect for the same reason as answer B.
Answer D is incorrect because TCP port 20 is used for the data connection on the server side, not the client side.
The correct answer is E, TCP port 20 on the client side. When the client initiates the data connection in passive mode, it uses TCP port 20 on its end to establish the data channel. The server uses a random port in a specified range for the data channel on its end.
