The related knowledge of FTP is as follows

FTP is a file transfer protocol that enables hosts to share files. FTP uses TCP to generate a virtual connection for control information and then a separate TCP connection for data transmission. The control connection uses a TELNET-like protocol to exchange commands and messages between hosts. File transfer protocol is a protocol for two computers to transfer files on TCP/IP network. FTP is one of the earliest protocols used in TCP/IP network and Internet, and belongs to the application layer of network protocol group. FTP clients can send commands to the server to download files, upload files and create or change directories on the server.

FTP is a protocol for two computers to transfer files on TCP/IP network. FTP is one of the earliest protocols used in TCP/IP network and Internet. Although the World Wide Web (WWW) has replaced most of the functions of FTP, FTP is still a way to copy files from clients to servers through the Internet. FTP clients can send commands to the server to download files, upload files and create or change directories on the server. The original FTP software was mostly operated by command line. With the graphical interface software such as CUTEFTP, it is convenient and simple to learn to use FTP transmission. Mainly used for "uploading". That is, transfer files to the server. Due to the fast transmission speed of FTP protocol, we like to use FTP when making websites such as "software download". At the same time, our service is public and does not require identity authentication, that is, "anonymous FTP server".

FTP is an application layer protocol, which is based on the transport layer and serves users. They are responsible for transmitting files. FTP is an 8-bit client-server protocol, which can operate any type of file without further processing, just like MIME or Unicode. However, the delay of FTP is very high, which means that the time from the initial request to the first receipt of the required data will be very long, and some lengthy login processes need to be carried out from time to time.

FTP service usually runs on ports 20 and 2 1. Port 20 is used to transmit data stream between client and server, and port 2 1 is used to transmit control stream, which is the entrance for commands to enter ftp server. When data is transmitted through the data stream, the control stream is in an idle state. When the control flow is idle for a long time, the client's firewall will set its session to timeout, which will cause some problems when a large amount of data passes through the firewall. At this point, although the file can be successfully transferred, some errors will occur in the transfer because the control session will be disconnected by the firewall.

The origin of FTP

In the network, it is often necessary to copy files from one computer to another computer in the distance. At first glance, this is a very simple thing, but it is actually a very difficult thing, because many computer application manufacturers have developed hundreds of file systems, and there are great differences.

In order to solve this contradiction, developers have developed related protocols to solve these problems. File sharing protocol I * * * can be divided into two categories: the first category is called online access, which means allowing multiple programs to access a file at the same time. Interested readers can refer to relevant literature, so I won't go into details here; The core of the second category is to copy the whole file. Both FTP of TCP and TFTP of UDP belong to this category. Their characteristic is that if you want to access a file, you must first get a copy of the local file. If you want to modify the file, you can only modify the file copy, and then send the modified file copy back to the original node.

strong function

Provide access to files (computer programs/data); Support indirect use of remote computers; So that users are not affected by the differences of various host file storage systems; Reliable and efficient data transmission. Although FTP can be directly used by end users, its application is mainly realized through programs. FTP control frame refers to TELNET exchange information, including TELNET commands and options. However, most FTP control frames are simple ASCII text, which can be divided into FTP commands or FTP messages. An FTP message is a response to an FTP command and consists of a reply code with explanatory text.