This document provides an overview of the File Transfer Protocol (FTP) including how it works, the types of connections it uses, common FTP commands, and an example of downloading a file from an FTP server. FTP uses TCP connections on ports 20 and 21, with port 21 for control commands and port 20 for transferring files. Common commands include get to download files, put to upload, cd to change directories, and bye to log off. The example demonstrates connecting to an FTP server and navigating directories to download a specific file.

1. By: Om Prakash
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This stands for File Transfer Protocol. This is the
simplest and most popular way to exchange files
over the Internet or intranet.

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 Transferring files from a client computer to a server computer
is called "uploading" and transferring from a server to a client
is "downloading".
To access an FTP server, users must be able to connect
to the Internet or an intranet (via a modem or local area
network) with an FTP client program.
FTP uses the services of TCP. It needs two TCP
connections. The well-known port 21 is used for the
control connection and the well-known port 20 for the
data connection

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5. CONTROL CONNECTION:
The communication path between the USER-PI (Process
Interpreter) and SERVER-PI for the exchange of
commands and replies. This connection follows the Telnet
Protocol.
DATA CONNECTION:
A full duplex connection over which data is transferred, in
a specified mode and type. The data transferred may be a
part of a file, an entire file or a number of files. The path
may be between a server-DTP (Data Transfer Process) and
a user-DTP, or between two server-DTPs.
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Client connect from a random unprivileged port (n > 1023) to the
servers command port (21) and sends port command to tell server to
connect to n+1 then listens on the next higher unprivileged port (n+1)
for server responses. The server connects from it’s data port (20) to the
client data port (n+1)
ClientServer
20 21 1026 1027
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Types of connections

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Client opens two random unprivileged ports ( n > 1023 and n+1; ex
1026 and 1027) and connects the first port (n) to server command port
21 and issues a PASV command (server sends port to use for data);
client connects to servers specified data port, server completes
connection.
ClientServer
20 21 1026 1027
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2024
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8. Internal client
Private FTP server
INTERNET
External client
Ways to connect to an FTP server
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9. Private user-only site
Allows only system users (or users with FTP profile) to connect
via FTP and access their files.
Anonymous
Allows anyone on the network to connect to it and transfer files
without having an account.
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10. FTP commands
ftp [host]
- open an ftp session with the specified Host machine.
open [host]
- Establish a connection to the specified host when you're already at
an ftp prompt.
user [username]
- Log into an ftp server when you're already connected in an ftp
session.
ls [remote-directory]
- Print a listing of the contents of remote-directory on the remote
machine. The listing includes any system-dependent information
that the server chooses to include.
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11. help [command]
- Print an informative message about the meaning of command. If
no argument is given, ftp prints a list of the known commands.
ascii
- Set the file transfer type to ASCII . Only use this transfer method
for text-files.
binary
- Set the file transfer type to support binary file transfer. Use this
transfer method for anything other than a textfile.
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12. cd [remote-directory]
- Change the working directory on the remote machine to remote-
directory.
lcd [directory]
- Change the working directory to directory on the local machine.
If no directory is specified, the user's home directory is used.
pwd
- Print the name of the current working directory on the remote
machine. Often times this includes printing the full path.
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13. put [local-file]
- Put (upload) local-file to the remote machine. No
wildcards!
get [remote-file]
- Retrieve (download) remote-file and store it on the
local machine. No wildcards! Can only get one file at a
time.
mput [local-files]
- Expand wild cards in the list of local-files given as
arguments and do a put for each file in the resulting
list. The list of files should be separated by spaces.
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14. mkdir [new-directory-name]
- create a directory new-directory-name on the
remote machine.
rmdir [directory-name]
- Delete the directory entitled directory-name on the
remote machine.
rename [old-file-name] [new-file-name]
- Rename the file old-file-name on the remote
machine, to the file new-file-name.
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15. quote site chmod xxx [file name]
- Change the permission modes of the file file-name
on the remote system to xxx mode. Note that the
chmod command is not always implemented.
get [file-name] "|more"
- Instead of downloading and saving the file file-name
on the local machine, you view its contents. Only
recommended to use with text files.
bye
- Terminate the FTP session with the remote server
and exit ftp. On Unix, an end of file should also
terminate the session and exit.
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Example…
Assume you are required to download the file
lan.txt
from
papa.cdrom.com/pub/games/

17. 1. At the command prompt type :
ftp papa.cdrom.com (this will start the ftp and
connection to the site)
The system will respond with the message
>connected to sunsite.cnlab-switch.ch.
>220 warchive.cdrom.com.FTP server (Version wu-
2.4.2(18)
>Thu nov 26 09:30:12 MET 2001) ready.
>Name (carchive.cdrom.com:usr):
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18. 2. Type ftp
The system will respond with something
similar to.
>331 Guest login ok, send your
complete e-mail address as password
>Password: (type your email)
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19. 3. After the welcome message that may look
something like this.
230 guest login ok, access restrictions apply.
Remote system type is UNIX.
We must now change to the directory “/pub/games”
Type in cd pub (this will change to the directory
pub), in this directory we will find downloadable
material.
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20. Lets type dir to see the list of files in there we should see
the directory games in the list.
drwxr-xr-x 6 731 730 512 Nov 4 05:11 games
The d in front of the listing tells me it is a directory.
If dir does not work we can use the command: ls-al
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21. 4. Use „cd‟ to change into the remaining
directories:
Type:
cd games
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22. 5. Use ‘dir’ to find the file:
Type:
dir l*
to get a listing of all files which start with ‘l’.
You should see:
-rw-rw-r– 1 2066 ftp-game 134868 Jun 30
2001 lan.txt
•Because there is no ‘d’ at the far left, you
know that it is a file, not a directory.
•The 134868 is the file size, it is 134,868
bytes (approx. 134 Kb). It was last
modified on the 30th of June 2001.
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23. 6. To download, type:
bin
• This will make your download in „binary‟ form
•This mode will always work for all files, whereas the
default mode „ascii‟ will only work for text files.
•Therefore always make sure you type „bin‟ before you
download or you may get garbage!
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24. Type:
get lan.txt
And type „y‟ when asked to confirm.
• „lan‟ will now download, and will soon be on the
computer you ran „ftp‟ from.
• Alternately, if you want to download multiple files,
you could type: „mget *‟, this would download *all*
files in the directory; „mget l*‟ would download all files
beginning with „l‟.
• If you do not wish to confirm each download one by
one, type „prompt‟ to turn that off. If you wish to have a
download indicator, type „hash‟.
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25. 6b. To upload:
• To upload a file you must be in a directory you are
allowed to upload into.
• You would type „put lan.txt‟ if you wished to upload
„lan.txt‟ or „mput l*‟ to upload all files beginning with
„l‟ for example.
• Make sure that you type „bin‟ again before you upload
anything.
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26. 7. Logging off.
Type:
bye
to close the connection and quit FTP.
• If you have any questions type either „man ftp‟
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