Internet Applications: Telnet, Ping and Traceroute

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Internet Applications Telnet, Ping and Traceroute

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Timesharing Systems

• Before Internet Multiple terminals attach to a
  single, time sharing computers
• a user interacts with the (timesharing) computer
  through its terminal
• Each individual user can choose which application
  to run
• Although applications are run remotely, input and
  output for the applications are displayed on the
  user terminal
• The timeshared computer can run several
  applications.

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Timesharing Systems (cont.)

• Because several users may work on a timesharing
  machine, the system requires
• An account be made for each legit user, which is
  given a unique name, called login identifier
• Each user has a password associated with its
  account
• In order to access the timeshared machine, a user
  has to enter its login identifier and
  password---the process is called logging in or
  login.
• After logging in, a user can run any application
• When a user is done, he logs out .

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Remote login (telnet)

• Achieves the same functionality as conventional
  login
• A user invokes telnet on a remote machine
• The remote machine asks for a login and a
  password
• The user can work on the remote machine as it
  does on a terminal connected directly with a
  timeshared machine.

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Telnet

• Follows the client-server paradigm
• The local applications is the client
• The remote application is the server
• The server has to be running before any client
  can begin
• Any data entered by the client is transmitted to
  the remote computer
• Any data produced by an application started by
  the user in question on the remote machine is
  displayed on the local machine

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Telnet (cont.)

• Uses TCP/IP for communication between client and
  server
• Telnet protocol part of TCP/IP specification
• How to submit login and password information
• How to terminate a session (type exit, for ex.)
• How to abort a session

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Telnet benefits

• Allows for performing computation on different
  machines
• Allows for a local user to use applications
  residing only on the remote machine
• ex. applications designed for a specific type
  of computer (ex Unix applications)
• Once a user is connected, he can work on the
  remote machine as if it were local

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Telnet benefits (cont.)

• Allows many users to access specific
  applications without having to modify the
  applications
• Ex a database applications, say Oracle, running
  on special computers, say IBM machines, cannot be
  installed on PCs running Microsoft Windows.
• However, any user on PC can use the database
  provided it has a valid account on the remote
  machine where the database is installed.
• Should the database software run before the
  client application started in order for a user to
  connect to it?

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Running telnet

• Start SSH Secure Shell Client
• Connect to acunix.albany.edu
• Enter your login name and password
• Commands that you can issue on acunix
• mkdir ltdirectory namegt --- creates a new
  directory
• ex mkdir public_html
• cd ltdirectory namegt ---makes the current
  directory the one specified in the command
• Ex cd public_html
• ls ---list the files in the current directory

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Running telnet (cont.)

• chmod ltrightsgt ltfile namegt change the rights to
  the file
• Ex chmod 644 index.html ---- makes file
  index.html readable and writable by owner, and
  readable by others
• chmod 755 /public_html/ --- makes the directory
  public_html modifiable by the user, and readable
  by everybody else.
• man ltcommand namegt---displays the functionality
  of the command given as parameter
• Ex man chmod
• more ltfile_namegt --- displays the content of the
  file given as parameter

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Running telnet (cont.)

• cat ltfilesgt --- concatenates the files given as
  parameters
• lpr ltfile-namegt --- prints the file given as
  parameter at the default printer

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A cautionary note

• When working remote, telnet uses the display,
  keyboard, and mouse on the users local computer,
• However the remote applications can only interact
  with the files and I/O devices of the remote
  computer

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Probing tools ping

• Sends messages to a remote host given as
  parameter and reports the result.
• Ex entering ping cs.rutgers.edu will display the
  status of that host, ex alive
• ping -s lthost namegt sends a datagram every
  second and displays the round trip time (the time
  between sending a message and receiving a
  response)

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Ping

• Ex try
• ping cs.columbia.edu
• ping cs.stanford.edu
• What do you notice?

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Ping (cont.)

• The average time increases with the distance
• Values of 40 ms are most common
• Values of hundreds of ms and/or packet loss mean
  that the path to the destination is congested
• However when no response is received ping cannot
  determine the reason
• Possible reasons for failure
• network failure or congestion,
• the remote computer can be off, or disconnected
  from the network, or discard ping messages.

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Probing tools traceroute

• Used to determine the intermediate computers
  along the path to a remote destination
• Ex traceroute dandelion-patch.mit.edu may
  produce the following result

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Traceroute (cont.)

• Each line---corresponds to an intermediate
  computer or hop
• Try
• traceroute cs.columbia.edu
• traceroute cs.stanford.edu