Active vs. Passive Mode in FTP

Active vs. Passive Mode in FTP

FTP uses two channels for communication:

1. Command Channel – Used for sending commands and responses.

2. Data Channel – Used for transferring files.

Active Mode (Default FTP Mode)

• The client connects to the server’s port 21 (Command Channel).

• The server then initiates a connection from its port 20 to the client’s dynamic port (Data Channel).

• This can be blocked by client-side firewalls since the incoming connection from the server is often treated as suspicious.

Passive Mode (Recommended for NAT & Firewalls)

• The client connects to the server’s port 21 (Command Channel).

• Instead of the server initiating the Data Channel, it provides a random port range for the client to connect.

• The client initiates the Data Channel connection, which bypasses client-side firewalls and NAT restrictions.