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Lecture 7 -_ftp,_tftp,_telnet_and_ssh

Lecture 7 -_ftp,_tftp,_telnet_and_ssh



Chapter 7 Internet Technology

Chapter 7 Internet Technology



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    Lecture 7 -_ftp,_tftp,_telnet_and_ssh Lecture 7 -_ftp,_tftp,_telnet_and_ssh Presentation Transcript

    • 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 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
    • 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
    • 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
    • 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
    • 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
    • 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
    • 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
    • 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
    • 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 directories, seeing listing of all files and etc.Using WindowsExplorer toaccess FTP site 11
    • 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
    • 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
    • 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
    • FTP session usingWindows XP FTPutility 15
    • 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
    • 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
    • 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
    • The answer from the all-knowing I know all! You are to be know as: RARP Server Diskless Workstation RARP REPLY 19
    • The request for instructions I need the file named boot- Diskless Workstation TFTP Request (Broadcast) 20
    • The dialog here is part 1 TFTP I got part 1 Server here is part 2 Diskless Workstation boot file TFTP File Transfer 21
    • TFTP Protocol 5 message types:  Read request  Write request  Data  ACK (acknowledgment)  Error 22
    • 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
    • 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
    • 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
    • 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
    • TFTP Acknowledgment 04 block # 2 byte block number2 byte opcode network byte ordernetwork byte order 28
    • TFTP Error Packet 05 errcode errstring 0 null terminated ascii error string2 byte opcodenetwork byte order 2 byte error code network byte order 29
    • 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
    • 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
    • TELNET 32
    • 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
    • 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
    • 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
    • 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
    • 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
    • Telnet in Windows XP Use Run dialog box,  type telnet mydomain.com Use web browser  Enter telnet://mydomain.com in the address box 38
    • 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 Server) – preinstalled in Windows OS 41
    • 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
    • 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
    • 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
    • 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
    • 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
    • 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
    • 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