16.4 Network Commands
16.4.2 Telnet
Another very useful TCP/IP utility is telnet, which is standard on the UNIX operating system. Telnet is a client-server terminal emulation program that allows you to connect to another system. The telnet server simulates a terminal in order to authorize a user or telnet client to connect to a remote system and work in that environment. When you telnet to another host, you are prompted for a use name and password. Once a session is established from your telnet client, you can enter commands as if you were entering them directly on the server console. You can telnet to several different hosts and have multiple telnet sessions open simultaneously.

All operating systems that support TCP/IP provide at least a telnet client. Not all operating systems provide a telnet server or daemon, however UNIX provides both. In addition to connecting to other hosts, telnet can also be used to connect to and manage network devices such as switches and routers. These devices are actually microcomputers with a CPU and RAM but they do not have a keyboard or monitor. Telnet allows you to use your computer's keyboard and monitor to remotely access and administer these devices.

Telnet is another good network troubleshooting tool. It is a non-graphical communications utility that can be used to check the upper layers of the OSI model. It runs at layer 7, the Application layer. If you are having trouble executing another, perhaps graphical, client-server application, you can try to telnet to the host or server to very that the TCP/IP protocol stack is functioning correctly. Remember, not all network operating systems support the telnet server function. For instance, you can telnet from a Windows 9x or NT/2000 workstation to a UNIX server, but you cannot telnet to the Windows workstation. The Windows operating system includes a telnet client but not a telnet daemon or server. As long as the host operating system is running a telnet daemon, you can telnet to it.

You can telnet to the name of a host computer if you have a naming service running such as Domain Name Service (DNS) or if you have entered the host name and IP address in your /etc/inet/hosts files. If not, you can telnet the IP address of the host. When using telnet, you can:

  • Open a session on a remote machine
  • Alternate between the remote session and the local session
  • Access machines that do not run under the UNIX environment


Figure shows an example of using telnet to connect to a remote system called beach. Notice that the host name beach is converted to an IP address using name to IP address resolution. You could also telnet directly to the IP address of the host if you know it. Figure is an example of using telnet to alternate between the remote session and a local session.
Interactive Media Activity (Flash, 95 kB)
  Using telnet

In this media activity, you are logged in as user2 and your current working directory is /home/user2. Type the commands that would accomplish the following objectives. 
Note: Be sure to press enter after each one. Click on step 1 to begin.