Understanding FTP

BUPT/QMUL2013-05-03

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Part1: Using telnet to learn FTP operations in passive mode

Steps:1. Using telnet to connect to given FTP server

$ telnet ftp.mayan.cn 21 2. login using username “mayan” and password “bupt”3. Input command “PASV”, calculate port number for data connections: port= p1×256+p2, p1 and p2 are taken from the server’s reply4. Using another terminal to set up data connection

$ telnet ftp.mayan.cn port5. Input command “LIST”

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Part1: Using telnet to learn FTP operations in passive mode

c:\>telnet ftp.mayan.cn 21

In another command window, setting up data connection 30*256+251

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In control connection:

In data connection:

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in control connection

in data connection

Change to lab directory and list

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Download lab2.pdf

in control connection

in data connection

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FTP commands to try

USER PASS PWD CWD LIST RETR STOR (trying on local FTP server) TYPE QUIT …

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Part2: Capture FTP commands and replies

Starting wiresharkset capture filter: tcp port 21 display filter: ftp

In your browser ftp://ftp.mayan.cnDownload a file, study the FTP commands and replies captured.

Active mode is used

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Part3: Learn to use FTP user command(1)

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Learn to use FTP user command(2)

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User commands used-example D:\ftp-test> ftp ftp.mayan.cn 21

Input user name and password ftp> ls ftp> get fork.c ftp> ren fork.c fork.txt ftp> ls ftp> binary ftp> ascii ftp> quit

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Control commands and replies used when logging in

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Commands and replies used for ls

Commands and replies used for get

One data connection persists for one file transfer

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The procedure of ls• Data connection establishment• Data transmission• Data connection close

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Rename fork.c fork.txt

ls

binaryascii

Release control connection