![]() In passive connections, the server sends its IP and port to the client with a "PASV" command then the client can try to connect the server with this IP. We all use antivirus software or Windows Firewalls, right? Now let's see passive mode. But it could be denied by the client because of firewalls. ![]() In active connections, clients send the IP and port to the server then the server will try to connect to the client. Active mode is a server based connection and passive is a client based connection. FTP servers can be run in "active" or "passive" mode. Send command, receive "OK" command, send data, receive data, and that's all. The numbers represent the code number and the optional text represents explanations (e.g., ) or needed parameters (e.g., )." So what do we need to do? It's so clear. "The server responds on the control connection with three digit status codes in ASCII with an optional text message, for example "200" (or "200 OK.") means that the last command was successful. ![]() Due to this two-port structure, FTP is considered an out-of-band protocol, as opposed to an in-band protocol such as HTTP." For example, "RETR filename" would transfer the specified file from the server to the client. The control connection is used for session administration (i.e., commands, identification, passwords) exchanged between the client and server using a Telnet-like protocol. It remains open for the duration of the session, with a second connection, called the data connection either opened by the server from its port 20 to a negotiated client port ( active mode) or opened by the client from an arbitrary port to a negotiated server port ( passive mode) as required to transfer file data. We can better understand FTP from Wikipedia: "The client computer is able to communicate with the server on port 21 and it's called the control connection. In order to do all of these, the FTP server needs to be running and waiting for incoming requests. For example, to send a file, we can use "stor" from the command line. We can still use " cmd.exe" to connect to FTP servers because FTP works with commands. And it's a client-server architecture.įTP programs were based on command-lines. We know FTP is a standard TCP based network protocol used to transfer files from one host to another host. FileZilla is good enough but it's not mine. So I decided to write my own application to handle all of this. I needed to connect to my server via FTP, send files, download files, etc. It all started when I tried to open my blog. FileZilla is so popular but it has some bugs. This program's interface look like FileZilla. So this Open Source project will lead your way when trying to learn about FTP. But we also need to understand FTP (File Transfer Protocol)'s substructure. ![]() I know there are a lot of FTP client programs available on the Internet.
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