FTP working mode

FTP Working modeFTP is the abbreviation of the file Transfer Protocol, which is used to transfer files between two computers. The FTP protocol is much more complex than HTTP. The complex reason is that the FTP protocol uses two TCP connections, one is a command link that is used to pass commands between the FTP client and the server, and the other is a data link for uploading or downloading data. The FTP protocol works in two ways: PORT and PASV, and Chinese meaning is active and passive.
Port mode:
FTP Server:tcp <------client:dynamic
FTP server:tcp------>client:dynamic PASV Mode:
FTP Server:tcp <----client:dynamic
FTP server:tcp Dynamic <----client:dynamic
The port (Active) connection process is that the client sends a connection request to the server's FTP port (the default is 21), and the server accepts the connection and establishes a command link. When the need to transfer data, the client on the command link with the port command to tell the server: "I opened the XXXX port, you come to connect me." The server then sends a connection request from Port 20 to the client's XXXX port, creating a data link to transmit the data. The PASV (passive) way of the connection process is that the client sends a connection request to the server's FTP port (the default is 21), the server accepts the connection, and establishes a command link. When you need to transfer data, the server tells the client on the command link using the PASV command: "I opened the XXXX port, you come to connect me." The client then sends a connection request to the server's XXXX port, creating a data link to transmit the data. Note: Choose to log on to the FTP server in PASV or PORT mode, and choose the FTP client instead of the FTP server. FTP common problems in AnalysisOne, unable to access FTP SERVER
The reason may be
1, the firewall has filtered the FTP request
2. The client enforces the use of the PASV mode connection, and FTP SERVER does not support or open PASV mode
3, the network can not access the second, the client can log on, but can not browse data
The reason may be
1, the client is in the intranet, and GATEWAY has no relevant settings to allow PORT MODE access to remote FTP SERVER
2, the client itself has a network limit of more than 1024 of their access to the port (such as: TCP/IP filtering)
3, the client use software does not open or support PASV MODE Access three, some can log in, some cannot log in
The reason is that the client that cannot log in does not use PASV MODE to access the FTP SERVER FTP access Error Troubleshooting steps1, to ensure that the FTP SERVER to 127.0.0.1 access to their own
2, to ensure that the FTP SERVER to use the IP access
3, confirm the client and server-side network unobstructed
4, verify that both sides of the firewall set up correctly
5, confirm the access mode of both sides is correct FTP solutions to common problemsOne, FTP SERVER has public network IP, and the front has firewall 1, on the fire wall Open 21 ports (default)
2, on the FTP SERVER to open PASV MODE support
3. Specify the port range used by PASV MODE on FTP SERVER
4, on the fire wall to open the corresponding PASV MODE required Port two, FTP SERVER in the Intranet 1, if there is a firewall, refer to the above settings
2, on the GATEWAY to do port mapping, map TCP 21 port to the FTP SERVER 21 port
3. Specify the port range used by PASV MODE on FTP SERVER
4. Additional ports on the GATEWAY to map 20 ports and PASV MODE using the port to FTP SERVER
Third, FTP CLIENT 1, on the firewall to allow access to the external 21 ports
2. Open 1024 ports on the fireproof wall to support FTP SERVER using port MODE to access extranet from intranet
3, open the FTP CLIENT to use the Software PASV mode support (IE default is not to use PASV mode)
Description 1, PASV MODE port range function:
When the client connects to the server in a PASV way, the server picks up a port in this port range to connect to the client. If not specified, the default is a random port of more than 1024. Description 2, IE open PASV MODE method: Control Panel->internet option-> Advanced tab-> enable passive FTP
Summary: After the installation of FTP SERVER problems, according to experience, using the following principles to set up to solve most of the problems
1. FTP SERVER enables and specifies the range of ports used by PASV MODE, if a firewall allows access to these ports on a fireproof wall
2, FTP client try not to use IE, IE is only a rough FTP client tool, the default does not open PASV MODE, access error information single
3, FTP CLIENT shutdown TCP/IP filtering
4, try to use PASV mode to access the FTP server, rather than PORT mode