TCP/IP Note 4. Application Layer (2) -- FTP

TCP/IP note 4. application Layer (2) -- FTP 1. FTP (File Transfer Protocol) File Transfer Protocol FTP only provides some basic services for File Transfer, it uses TCP reliable transport service. The main function of FTP is to reduce or eliminate the incompatibility of File Processing in different operating systems. 1.1 complexity of copying files in a network environment: (1) the formats of data stored by computers are different. (2) the directory structure of a file is different from the file naming rules. (3) the operating system uses different commands for the same file access function. (4) access control methods are different. FTP is an 8-bit client-server protocol that can operate on any type of files without further processing, just like MIME or Unicode. 2. Two Linked FTP services generally run on ports 20 and 21. Port 20 is used to transmit data streams between the client and the server, while port 21 is used to transmit the control flow and the command is imported to the ftp server. Benefits: (1) making the Protocol simpler and easier to implement. (2) You can also use the control connection when transferring files (for example, the customer sends a request to terminate the transmission ). 3 FTP advantages and disadvantages 3.1 advantages: (1) promoting file sharing (computer programs or data) (2) Encouraging indirect or implicit use of remote computers (3) shielding users from details of various file storage systems on different hosts (4) reliable and efficient data transmission 3.2 disadvantages: (1) plaintext transmission is used for both passwords and file content, this vulnerability may cause unwanted eavesdropping. (2) because a random port must be opened to establish a connection, it is difficult for the client to filter FTP traffic in active mode when the firewall exists. This problem is solved by using FTP in passive mode. (3) The server may be notified of a reserved port connecting to a third-party computer. Although FTP can be directly used by end users, it is designed to be controlled by the FTP client program. Anonymous services are enabled for many sites running FTP services. In this setting, users can log on to the server without an account. By default, the anonymous user name is "anonymous ". This account does not require a password. Although the user's email address is usually required as the authentication password, it is only some details or the email address is not determined at all, it depends on the configuration of the FTP server.