tyt06fi.htm

一个学习tcp/ip协议的教程

---> USER tparker

331 Password required for tparker.

Password:

---> PASS qwerty5

230 User tparker logged in.

---> SYST

215 UNIX Type: L8

Remote system type is UNIX.

---> Type I

200 Type set to I.

Using binary mode to transfer files.

ftp> ls

---> PORT 47,80,10,28,4,175

200 PORT command successful.

---> TYPE A

200 Type set to A.

---> LIST

150 Opening ASCII mode data connection for /bin/ls.

total 4

-rw-r-----  1 tparker  tpci    2803  Apr 29 10:46 file1

-rw-rw-r--  1 tparker  tpci    1286  Apr 14 10:46 file5_draft

-rwxr-----  2 tparker  tpci   15635  Mar 14 23:23 test_comp_1

-rw-r-----  1 tparker  tpci      52  Apr 22 12:19 xyzzy

Transfer complete.

---> TYPE I

200 Type set to I.

ftp> <Ctrl+d>

tpci_hpws1-2&gt;</FONT></PRE><P>You might notice in the previous code how the mode changes from binary to ASCII to send the directory listing, and then back to binary (the system default value). You can see how the two systems communicate to display the status messages that appear without the debugging option active.<BR><P>When FTP is used in a graphical user environment, you might be able to use a GUI-based tool. For example, NetManage's ChameleonNFS provides the FTP utility shown in Figure 6.8. In this case, the NFS client on the Windows for Workgroups machine has connected to a UNIX server. The Local side of the window shows the Windows machine, and the Remote side of the window shows the UNIX box's current filesystem contents. When using a GUI-based utility like this one, you can use the mouse and various buttons to transfer files back and forth between machines.<BR><P><B><A HREF=06tyt08.gif>Figure 6.8. Many operating systems have a GUI-based </B><B>FTP client.</A></B><BR><BR><A ID=E69E87 NAME=E69E87></A><H4 ALIGN=CENTER><CENTER><FONT SIZE=4 COLOR=#FF0000><B>FTP Third-Party Transfers</B></FONT></CENTER></H4><BR><P>FTP enables a transfer to occur through a third machine positioned between the client and the server. This procedure is known as a <I>third-party transfer</I> and is sometimes necessary to obtain proper permissions to access the remote machine. Figure 6.9 shows the schematic of a third-party transfer, with the control connection made through a third machine.<BR><P><B><A HREF=06tyt09.gif>Figure 6.9. A third-party FTP transfer.</A></B><BR><P>When setting up a third-party connection, the client opens the control connections between the remote machine and the second client that handles the control channel. Only the control channel goes through the second client, whereas the data channel goes directly between the two ends.<BR><P>When a transfer request is submitted, it is transferred through the second client, which checks permissions and then forwards the request to the server. The data transfer can take place directly, because the permissions were checked on the control channel.<BR><BR><A ID=E69E88 NAME=E69E88></A><H4 ALIGN=CENTER><CENTER><FONT SIZE=4 COLOR=#FF0000><B>Anonymous FTP Access</B></FONT></CENTER></H4><BR><P>FTP requires a user ID and password to enable file transfer capabilities, but there is a more liberal method of enabling general access to a file or directory, called <I>anonymous FTP.</I> Anonymous FTP removes the requirement for a login account on the remote machine, usually enabling the login anonymous with a password of either guest or the user's actual login name. The following session shows the use of an anonymous FTP system:<BR><PRE>

<FONT COLOR=#000080>tpci_hpws4-1&gt; ftp uofo.edu

Connected to uofo.edu.

220 uofo.edu FTP server (Version 1.7.109.2 Tue Jul 28 23:32:34 GMT 1992) ready.