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Understanding FTP

Understanding FTP. BUPT/QMUL 2013-05-03. 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”

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Understanding FTP

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  1. Understanding FTP BUPT/QMUL 2013-05-03

  2. 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 reply • 4. Using another terminal to set up data connection • $ telnet ftp.mayan.cn port • 5. Input command “LIST” 2

  3. Part1: Using telnet to learn FTP operations in passive mode 30*256+251 c:\>telnet ftp.mayan.cn 21 In another command window, setting up data connection 3

  4. In control connection: In data connection: 4

  5. Change to lab directory and list in control connection in data connection 5

  6. Download lab2.pdf in control connection in data connection 6

  7. FTP commands to try USER PASS PWD CWD LIST RETR STOR (trying on local FTP server) TYPE QUIT … 7

  8. Part2: Capture FTP commands and replies • Starting wireshark • set capture filter: tcp port 21 display filter: ftp • In your browser • ftp://ftp.mayan.cn • Download a file, study the FTP commands and replies captured. • Active mode is used 8

  9. Part3: Learn to use FTP user command(1) 9

  10. Learn to use FTP user command(2) 10

  11. 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 11

  12. Control commands and replies used when logging in 12

  13. Commands and replies used for ls Commands and replies used for get One data connection persists for one file transfer 13

  14. The procedure of ls • Data connection establishment • Data transmission • Data connection close 14

  15. Rename fork.c fork.txt ls binary ascii Release control connection 15

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