Tuesday, September 9, 2014

What is FTP?

FTP or File Transfer Protocol
"... is a standard network protocol used to transfer computer files from one host to another host over a TCP-based network, such as the Internet. FTP is built on a client-server architecture and uses separate control and data connections between the client and the server."
wikipedia.org

One reason why this is being replaced by other network protocol is in its exposure of the user password in plain text for a traditional FTP server. SSH and encrypted FTP sessions have replaced almost all new implementations these days.

Which ports are used by this service?
Standard ports used are port 20 (data) and 21 (command) but this may change depending on the server's settings. On the client FTP site, free standard ports higher than number 1023  is used.



This service by the FTP Server can provide active or passive connection and sometimes both. A simplified explanation in Slacksite.org entitled "Active FTP vs. Passive FTP, a Definitive Explanation" is a good read.

Typically, on the FTP server in Passive mode will require connection to several higher standard ports and this allows larger number of connections. In Active mode, limitation on the server is to how many connections can be done over that one port 20.

How to determine if its in Passive more?
After login to FTP server, type
quote PASV

How to establish connection to an FTP server?
Use an FTP client and enter the FTP server's URL. E.g. on Linux, to connect to the FTP server ftp.myserver.com

ftp ftp.myserver.com

-end-


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