Telnet

• Telnet allows you to connect to a remote machine.
• When you telnet, you specify a host name, such as oz.uc.edu, and a port, such as 22.
• The server reacts differently based on the port you use.  Port 80 is the default for HTTP (web documents).  FTP, mail, and time also have ports.  That way, when the server receives a request for a specific port, it knows how to react.
• The example in the book asks you to telnet to time-A.timefreq.bldrdoc.gov 13.  In this case, the host name is time-A.timefreq.bldrdoc.gov, and the port is 13, which is the port for time.  Try this out.
• One way to try: Choose Start-Run, and type telnet.  Choose connect-remote system.  Then you can put the host in the host name text field, and choose daytime in the port drop down.
• Alternatively, you can choose Start-Run, then type 'command' on Win 95, 98, Me, or 'cmd' on WinNT and Win 2000.  At the command prompt, type telnet time-A.timefreq.bldrdoc.gov 13
• You may also have telnet software on your menu that you can use.  If you telnet to oz from home, you can use SSH Secure Shell client.
• The service waiting on these ports is constantly waiting for a connection.  It only shuts down when it is stopped by an administrator on the server.
• Behind the scenes...
• Computers talk in IP addresses, which are similar to phone numbers.  You can either enter the IP address, or the domain name.  A computer called a Domain Name Server translates the domain name to the IP address if you choose the domain name.
• Want to find the IP address for oz?  Go to the command line, via cmd or command, and type ping oz.uc.edu   . Not only will this return the IP address, but it will also tell you how long it took to connect.
• Know the IP address but not the name?  Enter ping -a 129.137.2.91 .  If the DNS can reverse-resolve the name, it will return that to you along with the ping information.
• Want to find out how your computer talks to oz?  Type tracert oz.uc.edu .  This will show the computers that you are going through to get to oz.
• Want to know if the server is up?  A ping will return 'request timed out' if it is unable to reach a server, or if the server is down.

Created by:  Brandan Jones December 17, 2004