FTP Client Commands Guide
Understanding FTP Client Commands
The File Transfer Protocol (FTP) is a standard network protocol used for the transfer of computer files between a client and server on a computer network. Understanding FTP client commands is crucial for managing file transfers effectively and securely. This guide covers essential commands and concepts.
Common FTP Client Commands
Here are some of the most frequently used FTP client commands:
binary
- Sets the file transfer mode to binary, suitable for non-text files like images and executables.cd
- Changes the current working directory on the remote server.lcd
- Changes the current working directory on the local machine.get
- Downloads a single file from the remote server to the local machine.mget
- Downloads multiple files from the remote server.passive
- Enters passive transfer mode. This is generally preferred as it is more firewall-friendly.ls
- Lists the contents of the current remote directory.
FTP Ports and Transfer Modes
FTP utilizes two primary ports for its operations:
- Port 21: Used for control commands, establishing and managing the connection.
- Port 20: Used for data transfer.
Active Mode FTP
In active mode, the FTP client initiates a control session on port 21. For data transfer, the client opens a random port and tells the server which port to connect to. The server then uses port 20 to initiate the data connection back to the client's specified port. This can be problematic if the client is behind a firewall or NAT, as the server might be unable to establish the return connection.
Passive Mode FTP
Passive mode is more commonly used and generally more compatible with modern network setups. In this mode, the client initiates the control connection on port 21. When a data transfer is required, the server opens a random port and informs the client which port to connect to for the data transfer. The client then initiates the data connection to the server's specified port. This approach is often preferred by browsers and other applications because it avoids the inbound connection issues associated with active mode.
For more in-depth information on network protocols and security, refer to resources like the RFC 959, the official specification for FTP, or explore general network security guidelines from organizations like OWASP.