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HTWK 211D Lecture 6.1

HTWK 211D Lecture 6.1. FTP. What is FTP?. FTP – File Transfer Protocol FTP is a powerful protocol that allows files to be transferred from "computer A" to "computer B" or vice versa in a TCP/IP network (download/upload). FTP works on the client/server principle.

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HTWK 211D Lecture 6.1

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  1. HTWK 211DLecture 6.1 FTP

  2. What is FTP? • FTP – File Transfer Protocol • FTP is a powerful protocol that allows files to be transferred from "computer A" to "computer B" or vice versa in a TCP/IP network (download/upload). • FTP works on the client/server principle. • A client program enables the user to interact with a server in order to access information and services on the server computer. • Files that can be transferred are stored on computers called FTP servers.

  3. How FTP Works • The File Transfer Protocol is used to send files from one system to another under user commands. • FTP sets up a TCP connection to the target system for the exchange of control messages. • These allow user ID and password to be transmitted and allow the user to specify the file and file action desired

  4. Once file transfer is approved, a second TCP connection is set up for data transfer. • The file is transferred over the data connection, without the overhead of headers, or control information at the application level. • When the transfer is complete, the control connection is used to signal the completion and to accept new file transfer commands.

  5. Requirements for FTP • An FTP client installed on your computer (comes with most OS). Cute FTP (third party FTP software). • Information about the FTP server you want to connect to: • FTP server address.  This looks a lot like the address you type in Internet Explorer to browse websites.  One such example is "ftp.videodesk.net".  Sometimes the server address will be given as a numeric address, like "64.185.225.87". • User name and password required for the FTP connection.  Some FTP servers let you connect to them anonymously.  For anonymous connections, you do not need a user name and password.

  6. Active/Passive Mode • FTP server may support Active or Passive mode of connection, or both • Active FTP connection, the client opens a port and listens and the server actively connects to it.  • In a Passive FTP connection, the server opens a port and listens (passively) and the client connects to it. 

  7. Most FTP client programs select passive connection mode by default because server administrators prefer it as a safety measure. • Firewalls generally block connections that are "initiated" from the outside.  • Using passive mode, the FTP client (like Auto FTP Manager) is "reaching out" to the server to make the connection.  • The firewall will allow these outgoing connections, meaning that no special adjustments to firewall settings are required.  • Allowing active FTP would mean reducing the protection level of the firewall.

  8. If you are connecting to the FTP server using Active mode of connection you must set your firewall to accept connections to the port that your FTP client will open.  • For Passive FTP connection to succeed, the FTP server administrator must set his / her firewall to accept all connections to any ports that the FTP server may open. 

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