1. Introduction and principles
The beginning of the birth of the Internet there are three services: WWW, FTP, e-mail
FTP aimed at enterprise level, you can set permissions for data display different levels of permissions for different people.
But like network disk so basically no division of authority.
Summary:
FTP (File Transfer Protocol) file transfer protocol for two-way transmission control files online.
"Download" files is to copy files from a remote host on your computer
"Upload" file is the file from your computer to copy files to the remote host.
:( active mode here active and passive server is to say, the default mode is active)
Server initiates the connection from port 20 to the client
Passive mode:
The server within a specified range of a port passively wait for client connections
Firewall, I generally do not visit with your rules.
The client firewall may block the FTP server link (active mode)
FTP server port rule is controllable, will not cause the firewall to intercept (passive mode)
port:
FTP connection port :( active mode)
Control connections: TCP 21, for transmitting the FTP command information
Data connection: TCP 20, for uploading, downloading data
(Passive mode)
Control connections: TCP 21, for transmitting the FTP command information
Data connection: TCP random, for uploading, downloading data