FTP - File Transfer Protocol Explained

File Transfer Protocol (FTP) is a protocol that is part of the TCP/IP suite. It is the standard for transferring large amounts of data from server to server and from servers to clients. There is a very good chance that you have downloaded files from FTP sites many times, though it may have seemed you were only downloading from a website. FTP allows you to transfer files over a variety of hosts with different operating systems and file systems. There are so many FTP servers on the Internet, some are private with secure logon names, other ones are public with anonymous logins.

This paper will give a very brief outline of how the FTP Protocol functions and give the basic commands used during an FTP session. Keep in mind that these commands are generally automatic and are executed by either an FTP Client application, or done via your web browser. Though these methods are generally quicker than manually connecting to an FTP, it doesn't mean we should ignore the background behind how the technology works.

The FTP Protocol uses two connections to transfer a file. Each of these connections is quite a bit different, but work in conjunction with each other. The first connection is the Control Connection, which as the name implies controls the connection in regards to initiating the data streams and executing the commands. The second type of connection is the Data Connection, this connection is the actual connection that passes the files back and forth between the client and server.

Control Connection:
The control connection starts in a normal client / server manner. The client does an active open connection to port 21 of the FTP server to establish the control connection. The server is listening on port 21 for any active queries. Please keep in mind that though the primary FTP port is designated as porn 21, many servers, especially private ones are running on non-standard ports. The control connection as I mentioned early is the connection that allows you to pass commands between the client and server. Commands that must be sent are ones like LIST, STOR, and RETR. Once you enter a command on the control connection, you initiate the data connection.

Data Connection:
The data connection is spawned each time a file is moved between the client and server. The Control connection initiates the transfer with the PORT command, this tells the server to open an active connection to the clients passive port. The port command is typically the IP address followed by a 16 bit port number. The PORT command is issued in the following fashion:

PORT 24,82,116,92,4,150

That command should spawn a response of: 200 PORT Command Successful

After the PORT command has been initiated and is successful the next command in the data connection will be issued from the control connection. As I mentioned before this is typically a LIST, RERT or STOR. I will outline the basic FTP commands below for reference.

FTP Commands (Basic):
ABOR - Abort command and any data transfers
LIST - List the directory contents
PASS password - Used during authentication of login
USER username - Used during authentication of login
QUIT - Logoff / Quit session
RETR filename - Retrieve file from server STOR filename - Send a file to the server
SYST - Show System information
TYPE - Set the type of data, for instance ASCII
PORT - n1,n2,n3,n4,n5,n6 ( 1-4 = ip address, 5-6 port data)
HELP - Will give you additional available commands and more information

Reply Codes:
Reply codes are simply confirmations of things happening. One example of a reply code was went we got "200 PORT Command Successful" there are a handful of other reply codes, though generally the main ones are as follows.

125: Data Connection Open Start Transfer
200: Command OK
221: Goodbye / Terminate Connection
252: Write Error
331: Username OK, Enter Password
425: Can't Open Data Connection
500: Syntax Error on Command
501: Syntax Error on Arguments

Client Applications:
There are many different clients for FTP, and really it's up to personal taste in the end. A couple of the major ones are CuteFTP and FlashFXP. Personally I use FlashFXP when I'm in the Windows Environment. Just go to a freeware website or search on the search engines for a FTP Client and try a few out!

Summary of FTP:
The File Transfer Protocol is a wonderful and useful standard that has helped move data around the world safely and reliably for years. Everyone uses it from uploading their website to their web server, backing up their data to an off-site location, sharing their pictures with friends, or disseminating large data files for scientific research!

For even more information on the FTP, check out RFC 959.

Ken Dennis
http://KenDennis-RSS.homeip.net/

In The News:

Just Collect Less Data, Period.  The New York Times
Put Alexa and Siri to Work  The New York Times
12 Ways COVID-19 Will Change the Tech Industry  Kiplinger's Personal Finance
Can Our Phones Stop a Pandemic?  The New York Times

PDA Bible Free Download

Your Bible At Your FingertipsIt is fairly easy to find... Read More

Favorite Things To Do With Home Technology

Save money. Save 10-15% on utility bills per month. Work... Read More

Best PC Pocket GPS

Stop Getting LostOne of the greatest uses for a pocket... Read More

How I Started Working With 3D Modeling Programs

So I'll start from the very beginning.One day I was... Read More

Reliable File and Folder Sharing in Windows Xp

This tip is on sharing files and folders on a... Read More

An All Too Familar Pain

Lost & Found for the 21st CenturyIn today's hectic world... Read More

PC Tools Youd Never Think You Need

Do you use Windows standard uninstall feature? How do you... Read More

Cut Through the Hype and Make the Right Digital Camera Comparisons

There are soooo many choices. With all the styles and... Read More

Troubleshooting Computer Freeze (Lockup) Problems

How familiar does the following sound? Your computer was working... Read More

Protect Your PC from Viruses, Worms & Trojans

Each of the items in the checklist below is part... Read More

A Beginners Guide to Avoiding Viruses

"Aaaaaahhhhhh! I've been invaded by a virus!" Getting a virus... Read More

Desktop Security Software Risks - Part 2

This is the third in a series of articles highlighting... Read More

Dynamite Comes in Small Packages - Tiny Personal Audio MP3 Players Pack Powerful Music Enjoyment

MP3 players are Hot! Playing music has come a long... Read More

How to Buy a Plasma Television Set

Most people think that all you have to do to... Read More

How To Increase Computer Speed And Performance - Great Tips & Tricks

Many computer users are worried about their computer's performance. After... Read More

The Importance Of Email Backup

Viruses, software failures, power failures, human errors, hard drive failures... Read More

How To Buy An MP3 Player

Are you looking for an MP3 player but am not... Read More

What Has A Portable MP3 Player Have To Do With Your Business

Plenty! When we made the decision to be our own... Read More

How to Save an Image in a SQL Server Database?

Most of the web applications have a lot of images... Read More

Some Thoughts on Choosing a Flash MP3 Player

Flash mp3 players come with an exciting array of features,... Read More

Smart Apple iPod Tips and Techniques

Are you thinking of buying an Apple iPod? Or have... Read More

A Peek Into the Near Future of Electronics Technology

How long do you think DVDs have around? 20 years?... Read More

Use Your Computer For Your Entertainment Needs

By using your computer today you can find a lot... Read More

Linux Power Tools - Great Tools to Make System Administration Easy

World War II - Germany decided to attack Poland. Poland... Read More

MCSE 70-290 Certification Primer

Microsoft Certifications are one of the most widely acclaimed, pursued,... Read More