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The TCP/IP Guide

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Table Of Contents  The TCP/IP Guide
 9  TCP/IP Application Layer Protocols, Services and Applications (OSI Layers 5, 6 and 7)
      9  TCP/IP Key Applications and Application Protocols
           9  TCP/IP File and Message Transfer Applications and Protocols (FTP, TFTP, Electronic Mail, USENET, HTTP/WWW, Gopher)
                9  TCP/IP General File Transfer Protocols (FTP and TFTP)
                     9  File Transfer Protocol (FTP)
                          9  FTP Commands and Replies

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FTP Internal Protocol Commands and Command Groups
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FTP User Interface and User Commands
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FTP Replies, Reply Code Format and Important Reply Codes
(Page 1 of 5)

Each time that the User-PI sends a command to the Server-PI over the control connection, the server sends back a reply. FTP replies serve three main purposes. First, they serve as confirmation that the server received a command. Second, they tell the user device whether the command was accepted or not, and if an error occurred, what it was. Third, they communicate various types of information to the user of the session, such as the status of a transfer.

The Advantages of Using Both Text and Numeric Replies

For a human user, a string of reply text would be sufficient to satisfy the requirements above, and FTP replies do include descriptive text. But having only a text string would make it difficult or impossible for FTP software on the client side to interpret results coming from the server. FTP was designed to also allow software applications to interact with each other over the FTP command link. For this reason, the protocol designed its reply system around the use of reply codes.

FTP reply codes are three-digit numeric responses that can be easily interpreted by a computer program. They are also useful for human users who are familiar with FTP, because they communicate at a glance the results of various operations. While each FTP server implementation may differ in the text sent for each type of reply, the reply codes are used in a consistent manner based on the specifications of the FTP standard. It is therefore the codes that are examined to determine the results of a command; the text is just descriptive.


Previous Topic/Section
FTP Internal Protocol Commands and Command Groups
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Pages in Current Topic/Section
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2345
Next Page
FTP User Interface and User Commands
Next Topic/Section

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