What is Passive FTP?

FTP (File Transfer Protocol) is one of the protocols in the TCP / IP protocol group. The FTP protocol includes two components, one is an FTP server, and the other is an FTP client. The FTP server is used to store files. Users can use FTP clients to access resources located on the FTP server through the FTP protocol. When developing a website, the FTP protocol is usually used to transfer web pages or programs to a web server. In addition, due to the very high efficiency of FTP transfers, this protocol is also commonly used when transferring large files over the network.

FTP protocol

Same as most

FTP supports two modes, one is called Standard (that is, PORT mode, active mode), and the other is Passive (that is, PASV, passive mode). Standard mode FTP clients send PORT commands to the FTP server. Passive FTP client sends PASV command to FTP server.

Here's how these two methods work:

FXP said that the simple point is that one FTP client controls two FTP servers and transfers files between the two FTP servers. The full name of FXP is File Exchange Protocol. It can be considered that FXP itself is actually a subset of FTP, because FXP method actually uses the proxy command of the FTP server, but its prerequisite is that the FTP server must support PASV , And supports FXP mode.

During FXP transmission, the file is not downloaded to the local. The local only sends control commands. Therefore, the speed of FXP transmission is only between the two FTP servers.

The task of the FTP protocol is to transfer files from one computer to another. It has nothing to do with where the two computers are located, how they are connected, or even whether they use the same operating system. Suppose two computers talk through the ftp protocol and can access the Internet.

You can use the ftp command to transfer files. There are some minor differences in the use of each operating system, but the basic command structure of each protocol is the same.

There are two ways of FTP transmission: ASCII transmission mode and binary data transmission mode.

ASCII FTP protocol ASCII transmission mode

Assume that the file you are copying contains simple ASCII text. If you are running a different operating system on the remote machine, FTP will usually automatically adjust the content of the file when the file is transferred so that the file can be interpreted by another computer for storage. The format of the text file. However, it is often the case that the file being transmitted by the user does not contain a text file. They may be programs, databases, word processing files, or compressed files (although the word processing file contains most of the text, which also contains the indicated page size) , Fonts, and other non-printing characters).

Before copying any non-text files, use the binary command to tell ftp to copy verbatim, do not process these files, which is also the binary transmission described below.

FTP protocol binary transfer mode

In binary transfer, the bit order of the file is saved so that the original and the copied are mapped one-to-one. Even files containing bit sequences on the destination machine are meaningless. For example, macintosh transfers an executable file to a Windows system in binary mode. On the other system, this file cannot be executed.

If you transfer binary files in ASCII mode, they will be translated even if they are not needed. This can make transfers slightly slower, and can also corrupt data and make files unusable. (On most computers, the ASCII method generally assumes that the first significant bit of each character is meaningless, because ASCII character combinations do not use it. If you transfer a binary file, all bits are important.) If you know both The machine is the same, the binary mode is valid for both text files and data files.