telnet is used to communicate with another host using the TELNET protocol.
$ telnet telnet>
telnet can be used two main ways. The first is by simply typing
this will cause it to enter command mode which is indicated by the prompt
When in command mode it will accept a number of possible commands such as hostname, port, username, source IP address. Exit the command mode by typing
$ telnet telnet> open hostname.com
telnet can be used by specifing all the arguements in one line.
$ telnet -l user host.com:8000
This command will attempt to connect to remote host host.com on port 8000 using the login name user.
Common Use Cases
telnet is one of the first protocols for communicating between computers.
It is rarely used now because it sends messages unencrypted. Other
communication protocols such as
ssh are more secure and are used more
telnet can still be used to quickly check the connection to a
remote host before continuing communication using a more secure protocol. This
can be done with the command.
$ telnet host.com:8000
telnet can also be used to interactively follow a TCP stream. An example of that is shown here:
telnet is not completely obsolete however as it can be used to do incredible
things such as streaming a 20 minute ascii video of Star Wars 4!! Which can be
done by typing:
$ telnet towel.blinkenlights.nl 23
To give you a hint the video looks something like this:
8888888888 888 88888 88 88 88 88 88 88 8888 88 88 88 88888 88 88 888888888 88 88 88888888 88 88 88 88 888888 88 88 88 888 88888 888888 88 88 88 88 88 88 88 88 88 8888 88 88 88 88888 8888 888 888 888888888 88 88 88 88 88 88 88 88 8888888
Useful Options / Examples
-E Stops any character from being recognized as an escape character -K Specifies no automatic login to the remote system -a Attempt automatic login -d Sets the initial value of the debug toggle to TRUE. -l <user> Specify the user to try to connect with. -s <src_addr> Set the source IP address for the telnet connection to <src_addr> which can be an IP address of a host name. -x Turns on encryption of the data stream if possible. -y Suppresses encryption of the data stream. <host> Indicates the official name of the remote host. <port> Indicates a port number, if not specified the default telnet port is used.