FTP Data Connection Modes: Passive or Active

Q

What are the differences of Passive Mode and Active Mode used FTP Control Connection?

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A

FTP protocol supports two modes on how to establish a temporary data connection:

1. Passive Mode - If the FTP client wants to establish a new data connection in Passive Mode, it will request the FTP server to select a port and setup a UDP socket listener on that port. The server will reply back the selected port number to the client. The client will then request for a connection with the server on that port. After the connection is established, data can be transferred.

In other words, in passive mode, the FTP server plays the data connection listener role, and the FTP client plays the requester role.

2. Active Mode - If the FTP client wants to establish a new data connection in Active Mode, it will select a port and setup a UDP socket listener on that port. The client will then send the selected port number to the server. The server will request for a connection with the client on that port. After the connection is established, data can be transferred.

In other words, in active mode, the FTP client plays the data connection listener role, and the FTP server plays the requester role.

From data traffic point of view, passive mode and active mode pretty much the same. No matter who is the listener, the same amount data will be transferred between the client and the server.

However, from the network configuration point of view, if you are using a personal computer at home and running a FTP client tool, using the active mode requires your computer to be configured to listen to incoming UDP connection requests from the Internet is a big challenge.

This is why most FTP client tools default to use Passive Mode for data connections.

 

Understanding FTP (File Transfer Protocol)

⇒⇒FTP - Frequently Asked Questions

2016-12-24, 558👍, 0💬