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FTP - What is it?
FTP stands for File Transfer Protocol which is a client/server protocol that is used for the transfer of files via the Internet. FTP requires a server program and a client program.
One area where FTP proves very useful is in Website development i.e. you could use FTP to upload your files to the your Internet Web host server. In the case of SnugServer, those files would be uploaded to the Snug Web Server (SnugServer itself) via the Snug FTP Server.
You use an FTP client to connect to an FTP Server. The FTP client consists of a window split into 2 areas. Usually, the top area represents the FTP server folders and files and the bottom area consists of all the folders and files on the local computer. You can however, connect to a different FTP server by typing in it's name which usually starts with ftp://
To move/copy folder/files to/from the FTP Server; select them, and then simply drag and drop them.
When you log onto an FTP Server you are given certain access rights based on your username and password e.g. Read, Write, Delete authority. However, some users can be recognised as Anonymous FTP users whereby they do not need a password. The Rights you are allowed as an FTP account holder, are determined by the FTP Server administrator.
A Typical FTP Session
Login session:
The client program connects to an FTP sever on the internet. When a connection has been established, the FTP server sends a welcome message to the client.
Server: 220 Test FTP server ready. Reply with your user-name
Client: USER anonymous
Server: 331 User name OK. Please give your email address as password
Client: PASS c.scott@companyname.com
Server: 230 User logged in |
220, 331 and 230 in the above example are server 'Reply Codes'.
USER and PASS are client 'Commands'.
In the above exampe the FTP client and server are communicating using plain text. However, some FTP Servers (e.g. Snug FTP Server) encrypt the password using OTP (one time password) or S/KEY.
This way, a password is never actually transmitted. It sends a 'hash' of the password rather than the password itself. This 'hash' is never used again, hence the wording 'one time password'.
View file session
Allows the client to ask for a folder/file listing.
Client: TYPE A
Server: 200 Type set to A
Client: PASV
Server: 227 Entering passive mode (156,23,11,132,45,02)
Client: LIST
Server: 150 Opening ASCII mode data connection for /bin/ls
Server: 226 Transfer complete |
| TYPE A |
The client tells the server to send a folder/file listing as plain ASCII. |
| 200 Type set to A |
The server responds by telling the client that it has set the type to A. |
| PASV |
The client tells the server to create a new connection and listen out for a client connection. |
| 227 Entering passive mode (156,23,11,132,45,02) |
The server sends back its IP Address and a port number to use. |
| LIST |
The client issues a LIST command telling the server to give a folder/file listing. |
| 150 Opening ASCII mode data connection for /bin/ls |
The server tells the client that the listing is ready.
The client now connects the the IP Address given earlier and starts to get the data. |
| 226 Transfer complete |
The server issues this line when the entire listing has been given to the client. |
NOTE:
If the client wants to receive a particular file e.g. help.zip, it can issue the following command:
Client: RETR help.zip
FTP Active & Passive modes
FTP servers can operate in both active and passive modes.
Active mode:
1. the client tells the server the TCP (Transfer control protocol) port it is listening on.
2. the server opens a TCP connection from port 20 to the client's TCP port.
3. folder/file transfer occurs.
Passive mode:
1. the client informs the server that it is ready to transfer folders/files.
2. the server tells the client which TCP port it is listening on.
3. the client opens a TCP connection to the server TCP port.
4. folder/file transfer occurs.
User Comments
FTP File Transfer Protocol
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