What is the difference between Active and Passive FTP mode?

Imagine an FTP session as a two-way street: one lane for instructions ("control"), and another for data transfer.

Control Lane:

• Client connects to the server on port 21 (like hailing at the server's address).
• Client and server exchange orders: login, list files, etc. (like chatting about what to do).

Data Lane:

• Used for file transfers and directory listings.
• Two options for opening this lane:

Active Mode (Classic but Tricky):

• Client opens a "listening port" like a booth at a market.
• Server connects back to the client through this booth (imagine the server walking over).
• Can be blocked by firewalls and routers acting as strict bouncers.

Passive Mode (Modern and Firewall-Friendly):

• Server opens a temporary booth upon client request.
• Client walks over to the server's booth to transfer data.
• No need for the server to connect back, so firewalls and routers don't get suspicious.

Which Mode to Choose?

Passive mode is generally preferred nowadays due to its firewall-friendliness. Think of it as the smooth, one-way street that avoids hassles with gatekeepers.

Bonus Tip:

Modern firewalls can sometimes handle active mode too, acting like smart assistants who recognize FTP traffic and open the gates accordingly.