What is the difference between HTTP and FTP? - Quora

https://www.quora.com/What-is-the-difference-between-HTTP-and-FTP

https://www.quora.com/What-are-the-differences-between-passive-and-active-connections-in-FTP-1/answer/Nikhil-Panikkar 

 

In active mode, the data channel is established by the server, while in passive mode, it is the client that establishes the data channel. (The server is passive in this mode, hence the name.)

Active Mode

In active mode, the client lets the server know, on which port, it is listening for the data. The server then establishes the connection and transfers data on this channel.

The problem with this approach is that the client may be behind a firewall, and the firewall may not configured to accept connections from the server. This is very common, because the end user may not be experienced enough to configure his firewall.

This is where the passive mode helps.

Passive Mode

In passive mode, the client lets the server know, on which port it is listening for data. However, the server does not establish the connection. Instead it tells the client, on which port, it is sending the data from. The client then establishes the connection. The server then transfers data on this channel.