FTP

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FTP File Transfer Protocol
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• FTP is commonly run on two ports, 20 and 21.
• FTP run exclusively over TCP.
• FTP is separated into control and data
• Control commands
• Data file tranfers
• The control follows the same protocol as Telnet

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• FTP has 3 transmission modes
• Stream mode - The data is transmitted as a stream
  of bytes. EOF or EOR will be indicated by a
  two-byte control word the first byte all 1s the
  second byte 1 for EOR 2 for EOF 3 for both.
• Block mode The data is transmitted as a series
  of data blocks each preceded by a header

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-----------------------------------------------
- Descriptor Byte Count 8 bits 16
bits ----------------------------------------
--------

• The header has 3 bytes
• First byte called Descriptor Code
• 128 End of data block is EOR
• 64 End of data block is EOF
• 32 Suspected errors in data block
• 16 Data block is a restart marker
• Last two bytes are the block byte count

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Compressed mode

• Compressed mode has 3 type of data being sent
• regular
• Compressed
• Filler bytes (space)

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Compressed Mode

• Compressed mode has 3 type of data being sent
• Escape sequence

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Commands

• Various commands for your enjoyment
• User
• Pass
• Acct account
• Cwd change working directory
• Cdup
• Smnt mount different directory

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Commands

• Various commands for your enjoyment
• Rein restarts connection
• Quit logs out

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Commands

• TRANSFER PARAMETER COMMANDS
• Port
• Pasv requests the server to listen
• Type ascii /image
• Stru File structure (fie/record/page)
• Mode transfer mode (stream/compressed/block)

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Commands

• FTP SERVICE COMMANDS
• Retr retrieves the file
• Stor tells the server to upload the file and
  save it
• Stou same only different name
• Appe append the data to the file
• Allo asks the server to allocate space for the
  file to be uploaded
• And so on

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