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Unformatted text preview: /homenet2run/tcpip/tcp-ip-illustrated/ftp_file.htm (8 of 24) [12/09/2001 14.47.49] Chapter 27. FTP: File Transfer Protocol control connection (1173 in this example). This is OK, since the server's port numbers for
the two connections are different: one is 20 and the other is 21. Nevertheless, in the next
section we'll see why current implementations normally don't do this. 27.3 FTP Examples
We now look at some examples using FTP: its management of the data connection, how
text files are sent using NVT ASCII, FTP'S use of the Telnet synch signal to abort an
inprogress transfer, and finally the popular "anonymous FTP."
Connection Management: Ephemeral Data Port
Let's first look at FTP's connection management with a simple FTP session that just lists a
file on the server. We run the client on the host svr4 with the -d flag (debug). This tells
it to print the commands and replies that are exchanged across the control connection. All
the lines preceded by ---> are sent by the client to the server, and the lines that begin
with a 3-digit number are the server's replies. The client's interactive prompt is ftp>.
svr4 % ftp -d bsdi
Connected to bsdi.
220 bsdi FTP server (Version
---> USER rstevens
331 Password required for
---> PASS XXXXXXX
230 User rstevens logged in.
ftp> dir hello.c -d option for debug output
client does active open of control
server responds it is ready
client prompts us for a login name
we type RETURN, so client sends default we type our password; it's not echoed
client sends it as cleartext ask for directory listing of a single file
---> PORT 140,252,13,34,4,150 see figure 27.4
200 PORT command successful.
---> LIST hello.c
150 Opening ASCII mode data connection for /bin/ls.
-rw-r--r-- 1 rstevens staff 38 Jul 17 12:47 hello.c
226 Transfer complete.
output by client
56 bytes received in 0.03 seconds (1.8 Kbytes/s) file:///D|/Documents%20and%20Settings/bigini/Docum.../h...
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This test prep was uploaded on 04/04/2014 for the course ECE EL5373 taught by Professor Guoyang during the Spring '12 term at NYU Poly.
- Spring '12