[Nov 23, 2009 14:09] Web access to Microsoft Live@edu accounts now works.
Summary
FTP clients that use the standard mode of the FTP protocol are handled as expected by our dormitory network traffic shaping system. Data network traffic for these clients is not subject to shaping and operates at full speed. Microsoft Internet Explorer works using this standard mode and should be recommended for use when downloading data over the Internet using FTP.
The FTP protocol also has a passive (PASV) mode of operation. FTP clients using passive mode cannot be detected by our traffic shaping rules and their traffic is shaped by the system. Netscape Communicator uses passive mode and should be avoided when downloading files over the Internet using FTP.
What FTP clients to use
Listed are the FTP clients recommended to use for best FTP throughput. All should have passive (PASV) mode disabled.
- AbsoluteFTP
- Internet Explorer FTP
- Microsoft FTP
- SecureFX
- UNIX FTP
- WS_FTP
Technical Details
The FTP protocol uses two different channels for communication between the client and the server. The initial connection is established when the client opens a control channel connection to port 21 of the server. Data transfer operates over a second channel that is established each time a new chunk of data is sent. The normal mode for the data channel is to use port 20, the ftp-data port. Whenever either the local port or the remote port on the data channel is port 20, the dorm network traffic shaping works as desired and does not limit FTP throughput.
A second passive mode of the FTP protocol exists. This mode was not widely used until the advent of some types of firewalls. The end result of a transfer in passive FTP mode is that the data channel uses random port numbers on both ends of the network connection. The use of random port numbers means that the traffic shaping system cannot detect that the data stream is FTP traffic and the channel is shaped.
| Example port usage for common UVa FTP clients | |||||
|---|---|---|---|---|---|
| FTP Client Name | Control Channel | Data Channel | Shaping OK | ||
| Local Port | Remote Port | Local Port | Remote Port | ||
| AbsoluteFTP | 1050 | 21 | 1067 | 20 | Yes |
| Internet Explorer FTP | 1129 | 21 | 1130 | 20 | Yes |
| Microsoft FTP Client | 1049 | 21 | 1057 | 20 | Yes |
| SecureFX FTP | 1064 | 21 | 1067 | 20 | Yes |
| Unix FTP | 44116 | 21 | 44118 | 20 | Yes |
| WS FTP | 1078 | 21 | 1079 | 20 | Yes |
| AbsoluteFTP (in PASV FTP mode) |
1050 | 21 | 1055 | 44121 | No |
| Netscape FTP | 1108 | 21 | 1119 | 20409 | No |
| WS FTP (in PASV FTP mode) |
1027 | 21 | 1031 | 44122 | No |
| SecureFX FTP (in PASV FTP mode) |
1352 | 21 | 1355 | 44125 | No |