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Chapter 6 Telnet and FTP

  1. Telnet - provides remote login or virtual terminal capability across a network [through TCP port #23] (client/server)
    • Telnet Connections - uses a network virtual terminal (keyboard & printer)
      telnet 192.132.89.3 (merlin)
      CTRL-D or the break sequence (CTRL-]) to exit [lo on our VAX]
      to allow client and server to use a GUI, need additional commands [e.g. xhosts+ setenv DISPLAY tpci_server:0.0]
    • Telnet Commands (used by the protocol, not the user)
      The Telnet command structure
      Interpret As Command(IAC) Command Code Options
    • TN3270 (used for EBCDIC systems)

  2. File Transfer Protocol (FTP)
    • FTP Commands(used by the protocol, not the user)

      FTP internal commands examples
      Command Description
      ABORAbort previous command
      HELP Retrieve information
      USER User ID

      FTP reply code first digits
      First Digit Description
      1 Action initiated
      2 Action completed
      3 Command accepted but on hold due to lack of info
      4 Command not accepted or completed (can reissue command)
      5 Command not accepted or completed (reissuing command will give same error)

      FTP reply code second digits
      Second Digit Description
      0 syntax error or illigal command
      1 reply to request for info
      2 reply toat refers to connection management
      3 reply for authenitication command
      4 not used
      5reply for status of server

    • FTP Connections (requires IP address or domain name; still logically on client)
      1. login
      2. define directory
      3. define file transfer mode (ASCII or BINARY)
      4. Start data transfer
      5. stop data transfer

      FTP user commands examples
      FTP command Description
      ascii Switch to ASCII mode
      cd change directory on server
      close terminate connection
      get fetch file from server
      open connect to server
      bye logout

    • FTP Third-Party Transfers
    • Anonymous FTP Access
    • FTP Servers (on UNIX, requires entry in /etc/inetd.conf to activate the ftpd)

  3. Trivial File Transfer Protocol (TFTP) (uses UDP and does not log onto server)
    used to load applications in diskless machines for bootstrapping
    uses port 69
    • TFTP Commands
      TFTP's Command Set
      TFTP command Description
      binary USes binary mode for transfers
      connect Determines the remote's address
      get retrieves a file from the remote
      put transfers a file to the remote
      trace displays protocol codes
      verbose displays all info

    • TFTP Packets (encapsulated in UDP headers)
      TFTP Protocol Data Unit Codes
      Code OpCode Description
      RRQ 1 Read request
      WRQ 2 Write request
      DATA 3 Send data
      ACK 4 Acknowledgment
      Error 5 Error

      because there is no connection between client/server, client sets a timer and waits for ACK

  4. Simple Mail Transfer Protocol (SMTP) (uses port # 25)
    • uses program like sendmail to implement SMTP; users use program like mail
    • SMTP uses spools / queues; returns undelivered mail

    • SMTP Commands (all messages transferred as 7-bit ASCII with a period ending the message)

  5. The Berkeley Utilities
    • The hosts.equiv and .rhosts Files (keeps list of "equivalent" hosts)
    • rlogin - enables user to log into another machine
    • rsh - lets you execute commands on a remote machine
    • rcp - lets you copy files across the network
    • rwho - displays a list of users on the network
    • ruptime - displays a list of all machines on the network, their status, # of active users, current load, & elaspsed time since system was booted
    • rexec - similar to rsh but uses an encrypted password.

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