Lecture 7:File Transfer andRemote File AccessBITS 2513INTERNET TECHNOLOGY                      1
Using FTP to Transfer Files   Web servers (using HTTP) and e-mail software    (using SMTP) must encode data so it appears...
Using FTP to Transfer Files (cont.)   FTP can transfer binary files over the Internet    without the encoding and decodin...
Using FTP to Transfer Files(cont.)   Large organizations might maintain several FTP sites in    different parts of the wo...
How FTP Works   An FTP server identifies users on an FTP site by their    user IDs.   FTP client and server software cre...
How FTP Works (cont.)   FTP client and server software can access their    individual file system and transfer files in e...
How FTP Works (cont.)   FTP server usually listen at port 21 for client    activity   Most Web servers have FTP service ...
Requirements for using FTP   An FTP client installed on the computer.   Login details of the FTP server to which you wan...
FTP Via a Web Browser   Have you ever attempted to download software    from a Web site and clicked a hyperlink that    s...
How to use FTP   Logging on to an FTP site with a Web browser                                                   10
How to use FTP      When you log on to an FTP site, you can browse through the       available files by changing director...
How to use FTP   An error occur when you attempt to upload a file to an    FTP site where you don’t have write permission...
FTP from a Command Prompt   Most operating systems, including Windows 9x,    Windows NT, Windows 2000, and Windows XP,   ...
FTP from a Command Promptcont.)   Another protocol similar to FTP is TFTP (Trivial    FTP).   TFTP has fewer commands th...
FTP session usingWindows XP FTPutility                    15
FTP CommandsOpening and closing connection ftp - starts an FTP session open hostname - connects to the specified host c...
Trivial File Transfer Protocol:TFTP Usage and Design   Transfer files between processes.   Minimal overhead (no security...
Diskless Workstation Booting 1The call for help                   Help! I dont know who I am!                   My Etherne...
The answer from the all-knowing   I know all! You are to be know as:                                         RARP   128.11...
The request for instructions                   I need the file named                    boot-128.113.45.211      Diskless ...
The dialog              here is part 1                                                TFTP                    I got part 1...
TFTP Protocol      5 message types:         Read  request         Write request         Data         ACK (acknowledgme...
Messages   Each is an independent UDP Datagram   Each has a 2 byte opcode (1st 2 bytes)   The structure of the rest of ...
Message Formats OPCODE      FILENAME   0      MODE     0 OPCODE    BLOCK#           DATA OPCODE    BLOCK# OPCODE    BLOCK#...
Read Request      01                filename            0            mode                  0             null terminated a...
Write Request      02                filename            0            mode                  0             null terminated ...
TFTP Data Packet         03          block #                  data 0 to 512 bytes                2 byte block number      ...
TFTP Acknowledgment                     04      block #                          2 byte block number2 byte opcode         ...
TFTP Error Packet         05          errcode                   errstring                  0                              ...
TFTP transfer modes   “netascii” : for transferring text files.     alllines end with rn (CR,LF).     provides standard...
NetAscii Transfer Mode         Unix - end of line marker is just n   receiving a file       you need to remove r before ...
TELNET         32
Initiating and Using TelnetSessions   Telnet enable user to;     create   a remote command console session on a host.   ...
Telnet   Telnet is a protocol used to pass commands    and replies between the client the UNIX    computer.   All UNIX s...
How Telnet Works   To use Telnet you need to know IP address of    the host where the resource you want to use   When yo...
How Telnet Works   You can start the service manually every time    you want to connect to a host,   Or you can configur...
How Telnet Works   When run a Telnet client, it makes a connection request    to the host (Telnet server).   If a Telnet...
Telnet in Windows XP   Use Run dialog box,     type   telnet mydomain.com   Use web browser     Enter   telnet://mydom...
Telnet in DOS prompt                       39
Telnet in HyperTerminal                          40
Examples of TELNET client/server   Tlntsvr.exe (Telnet Server) - preinstalled in    Windows OS   Telnet.exe (Telnet Serv...
Telnet Commands   open - to open hostname port number to    establish a Telnet connection to a host.   close - to close ...
Telnet Limitations   Telnet is a character-based communication    protocol and not designed to transmit cursor    movemen...
Telnet Limitations (cont.)   By default, Telnet does not encrypt any data    sent over the connection (including password...
Using Secure Shell (SSH) Protocol   SSH enables two computer to negotiate and    establish secure connection that use enc...
Using SSH Protocol (cont.)   It uses public-key cryptography to authenticate the    remote computer and to allow the remo...
Summary   FTP sites can be accessed by client software,    such as Web browsers, operating system    command utilities, o...
Summary (cont.)   Telnet program runs on the computer and    connects PC to a server on the network.   Enter commands th...
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Lecture 7 -_ftp,_tftp,_telnet_and_ssh

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Lecture 7 -_ftp,_tftp,_telnet_and_ssh

  1. 1. Lecture 7:File Transfer andRemote File AccessBITS 2513INTERNET TECHNOLOGY 1
  2. 2. Using FTP to Transfer Files Web servers (using HTTP) and e-mail software (using SMTP) must encode data so it appears as text when it travels over the Internet. FTP (File Transfer Protocol) offers an alternative. An FTP site is a computer running an FTP server application. On FTP server a program called daemon allows to download and upload files 2
  3. 3. Using FTP to Transfer Files (cont.) FTP can transfer binary files over the Internet without the encoding and decoding overhead, making it a popular protocol for moving files over the Internet. FTP also use to upload files from your computer to another computer on the internet 3
  4. 4. Using FTP to Transfer Files(cont.) Large organizations might maintain several FTP sites in different parts of the world to speed up download time across the globe. These are called mirror sites. A mirror site is a server that contains the same set of files as a heavily used server to off-load some of the burden of providing the files to the community using them. Mirror sites also serve as a backup for the main server in case the main server fails. 4
  5. 5. How FTP Works An FTP server identifies users on an FTP site by their user IDs. FTP client and server software create a session after you are logged on. The FTP client has access to the file system on the server. The local computer (the client) issues character-like commands, and the remote computer (the server) replies with numbers that are interpreted by the local computer. 5
  6. 6. How FTP Works (cont.) FTP client and server software can access their individual file system and transfer files in either direction Local host Remote host File FTP FTP File System Client Server System 6
  7. 7. How FTP Works (cont.) FTP server usually listen at port 21 for client activity Most Web servers have FTP service running to receive changes to Web pages files from web developers FTP server normally run on the same computer that is running a Web server 7
  8. 8. Requirements for using FTP An FTP client installed on the computer. Login details of the FTP server to which you want to connect:  The FTP server address. This looks a lot like the address you type in Internet Explorer to browse websites. One such example is “ftp://ftmk.kutkm.edu.my”.  The user name and password required for the FTP connection. Some FTP servers let you connect to them anonymously. For anonymous connections, you do not need a user name and password. 8
  9. 9. FTP Via a Web Browser Have you ever attempted to download software from a Web site and clicked a hyperlink that says “Click here to download now” or a similar message? If you carefully note the URL after you click to download the software, you will see that the protocol changes from http:// to ftp:// in the Web browser’s Address box. 9
  10. 10. How to use FTP Logging on to an FTP site with a Web browser 10
  11. 11. How to use FTP  When you log on to an FTP site, you can browse through the available files by changing directories, seeing listing of all files and etc.Using WindowsExplorer toaccess FTP site 11
  12. 12. How to use FTP An error occur when you attempt to upload a file to an FTP site where you don’t have write permission 12
  13. 13. FTP from a Command Prompt Most operating systems, including Windows 9x, Windows NT, Windows 2000, and Windows XP, offer FTP client software that runs from a command prompt. A batch file is a file with a .bat file extension that contains a list of DOS-like commands that can be executed as a group. 13
  14. 14. FTP from a Command Promptcont.) Another protocol similar to FTP is TFTP (Trivial FTP). TFTP has fewer commands than FTP and can be used only to send and receive files. It can be used for multicasting in which a file is sent to more than one client at the same time using the UDP (User Datagram Protocol). 14
  15. 15. FTP session usingWindows XP FTPutility 15
  16. 16. FTP CommandsOpening and closing connection ftp - starts an FTP session open hostname - connects to the specified host close - closes the connection (but not the FTP session!) quit - terminates the FTP sessionBrowsing on a remote machine dir - gives a full directory listing on the remote machine dir test* - displays only files and directories whose name begins with "test..." ls - same as dir, but provides a simplified listing of filenamesDirectories in FTP pwd - prints the name of the current remote directory cd remote-directory - changes working directory on remote host cd .. - moves up one level in the directory structure on the remote host lcd directory - changes the default directory on local host 16
  17. 17. Trivial File Transfer Protocol:TFTP Usage and Design Transfer files between processes. Minimal overhead (no security). Designed for UDP, although could be used with many transport protocols. Easy to implement Small - possible to include in firmware Used to bootstrap workstations and network devices. 17
  18. 18. Diskless Workstation Booting 1The call for help Help! I dont know who I am! My Ethernet address is: 4C:23:17:77:A6:03 RARP Diskless Workstation 18
  19. 19. The answer from the all-knowing I know all! You are to be know as: RARP 128.113.45.211 Server Diskless Workstation RARP REPLY 19
  20. 20. The request for instructions I need the file named boot-128.113.45.211 Diskless Workstation TFTP Request (Broadcast) 20
  21. 21. The dialog here is part 1 TFTP I got part 1 Server here is part 2 Diskless Workstation boot file TFTP File Transfer 21
  22. 22. TFTP Protocol 5 message types:  Read request  Write request  Data  ACK (acknowledgment)  Error 22
  23. 23. Messages Each is an independent UDP Datagram Each has a 2 byte opcode (1st 2 bytes) The structure of the rest of the datagram depends on the opcode. 23
  24. 24. Message Formats OPCODE FILENAME 0 MODE 0 OPCODE BLOCK# DATA OPCODE BLOCK# OPCODE BLOCK# ERROR MESSAGE 0 2 bytes 2 bytes 24
  25. 25. Read Request 01 filename 0 mode 0 null terminated ascii string null terminated ascii string containing name of file containing transfer mode2 byte opcodenetwork byte order variable length fields! 25
  26. 26. Write Request 02 filename 0 mode 0 null terminated ascii string null terminated ascii string containing name of file containing transfer mode2 byte opcodenetwork byte order variable length fields! 26
  27. 27. TFTP Data Packet 03 block # data 0 to 512 bytes 2 byte block number network byte order2 byte opcode all data packets have 512 bytesnetwork byte order except the last one. 27
  28. 28. TFTP Acknowledgment 04 block # 2 byte block number2 byte opcode network byte ordernetwork byte order 28
  29. 29. TFTP Error Packet 05 errcode errstring 0 null terminated ascii error string2 byte opcodenetwork byte order 2 byte error code network byte order 29
  30. 30. TFTP transfer modes “netascii” : for transferring text files.  alllines end with rn (CR,LF).  provides standard format for transferring text files.  both ends responsible for converting to/from netascii format. “octet” : for transferring binary files.  no translation done. 30
  31. 31. NetAscii Transfer Mode Unix - end of line marker is just n receiving a file  you need to remove r before storing data. sending a file  you need to replace every n with "rn" before sending 31
  32. 32. TELNET 32
  33. 33. Initiating and Using TelnetSessions Telnet enable user to;  create a remote command console session on a host.  run command line programs, shell commands, and scripts in a remote command console session just as though you were locally logged on to the host and using a local command prompt window. 33
  34. 34. Telnet Telnet is a protocol used to pass commands and replies between the client the UNIX computer. All UNIX systems support some form of Telnet. Windows versions also include Telnet Client and Telnet Server components. 34
  35. 35. How Telnet Works To use Telnet you need to know IP address of the host where the resource you want to use When you contact the host, the distant computer and your computer negotiate how to communicate with each other When client and server communicate they use Telnet protocol 35
  36. 36. How Telnet Works You can start the service manually every time you want to connect to a host, Or you can configure the service so that it starts every time your computer starts. Telnet clients cannot connect to a host unless a Telnet server program (or service) is running and listening for connection requests. 36
  37. 37. How Telnet Works When run a Telnet client, it makes a connection request to the host (Telnet server). If a Telnet server responds to the request, the Telnet client and server negotiate the details of the connection, such as flow control settings, window size, and terminal type. After the connection details are successfully negotiated, and logon credentials are validated, the Telnet server program creates a Telnet command console session. 37
  38. 38. Telnet in Windows XP Use Run dialog box,  type telnet mydomain.com Use web browser  Enter telnet://mydomain.com in the address box 38
  39. 39. Telnet in DOS prompt 39
  40. 40. Telnet in HyperTerminal 40
  41. 41. Examples of TELNET client/server Tlntsvr.exe (Telnet Server) - preinstalled in Windows OS Telnet.exe (Telnet Server) – preinstalled in Windows OS 41
  42. 42. Telnet Commands open - to open hostname port number to establish a Telnet connection to a host. close - to close an existing Telnet connection quit - to exit from Telnet status - to determine whether the Telnet client is connected. 42
  43. 43. Telnet Limitations Telnet is a character-based communication protocol and not designed to transmit cursor movements or GUI information. Can only run command line programs, shell commands, scripts, and batch files Some editing programs, such as vi and Edit, can be run over a Telnet connection However, these interactive programs are not true GUI programs because cursor movement is controlled by the keyboard, not the mouse. 43
  44. 44. Telnet Limitations (cont.) By default, Telnet does not encrypt any data sent over the connection (including passwords), and so it is trivial to eavesdrop on the communications and use the password later for malicious purposes. Lacks an authentication scheme that makes it possible to ensure that communication is carried out between the two desired hosts 44
  45. 45. Using Secure Shell (SSH) Protocol SSH enables two computer to negotiate and establish secure connection that use encryption May stop cracker who try to sniff password and data Provide secure communication for doing email, accessing Web, login to remote site and publishing file in FTP (SFTP) 45
  46. 46. Using SSH Protocol (cont.) It uses public-key cryptography to authenticate the remote computer and to allow the remote computer to authenticate the user SSH provides confidentiality and integrity of data exchanged between the two computers using  encryption  message authentication codes (MACs). PuTTY is a free SSH client and multiplatform - establish a secure channel between a local and a remote computer 46
  47. 47. Summary FTP sites can be accessed by client software, such as Web browsers, operating system command utilities, or GUI software dedicated to FTP, such as WS_FTP Pro. FTP also can be accessed from a command prompt. 47
  48. 48. Summary (cont.) Telnet program runs on the computer and connects PC to a server on the network. Enter commands through the Telnet program and they will be executed as if you were entering them directly on the server console. Enables you to control the server and communicate with other servers on the network 48
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