Contrary to the use of an active data connection, the passive data transfer reverses the direction of establishment of the data connection. Instead of issuing a PORT command, the client issues a PASV command, which uses no parameters. Upon accepting this command, the FTP server sends back a reply containing an IP address and port number. The client initiates a connection back to the server on the indicated IP address and port. An example of this sequence is illustrated in Fig.2.
Fig.2. The passive data connection
One of the reasons to use a passive data transfer is to bypass firewall configurations that block active data connections. For this reason, passive mode is often referred to as “firewall friendly mode.” An example of such a scenario is a firewall that has been configured to block any inbound attempts to open a connection. In this example, an FTP server responding to a client’s PORT command would receive an error when trying to open a connection to the indicated IP address and port. However, by using passive mode, the client initiates the connection from within the network, and the firewall allows the data transfer to proceed.
One of the reasons to use a passive data transfer is to bypass firewall configurations that block active data connections. For this reason, passive mode is often referred to as “firewall friendly mode.” An example of such a scenario is a firewall that has been configured to block any inbound attempts to open a connection. In this example, an FTP server responding to a client’s PORT command would receive an error when trying to open a connection to the indicated IP address and port. However, by using passive mode, the client initiates the connection from within the network, and the firewall allows the data transfer to proceed.
Explain the working for passive data connection in FTP.
Reviewed by enakta13
on
October 03, 2012
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Reviewed by enakta13
on
October 03, 2012
Rating: