While Telnet was, many, many, years ago,
a very popular tool for administering remote servers,
these days, largely because it transmits data between nodes in plain text,
it's rarely used.
I'll use Wireshark to show you exactly what I mean by plain text and
why such transmissions can be appallingly dangerous.
I've installed the Telnet package on this client and the Telnet server
package on the Linux server with the IP address 10.
0.
3.
234.
It's a throwaway LXE virtual container that I'm using just for this demo.
If you're working on a Windows machine,
you can enable Telnet by navigating to the Turn Windows
features On or Off menu in Programs and Features,
and checking the Telnet Client box.
Now, from a Linux client container, I'll enter the Telnet shell by typing telnet.
I'll return to this terminal in just a moment.
But first I'll open Wireshark,
select the lxcbr0 network bridge that my server uses
and start and start a live capture.
Now, back in the Telnet shell, I'll launch a new remote Telnet session on the 10.
0.
3.
234 server.
Dash l points to my remote login name, which is ubuntu,
and I'll follow that with the remote IP address.
The server responds to a request for a Password,
which I'll type in, and I'm given a remote command prompt.
I'll type a simple ls command just to show how it
would be displayed in Wireshark.
Let's head back to Wireshark, where there's obviously been plenty of action.
I'll highlight any of the Telnet packets in the top panel,
and then as I did for SSH in an earlier clip,
right-click and select Follow TCP Stream.
This time, there isn't nearly so much gibberish; in fact,
you can see the results of my ls command,
my login name, and the horror, my password in text.
That's how easy it can be for anyone with access to any
network between you and your remote target to grab
absolutely anything from your session.
So then why would anyone want to use Telnet these days?
Well you can use Telnet as a simple way to test network
connectivity and open ports to see whether,
say, the secure HTTP Port 443 is open on a server,
you can try quickly gaining access using that port from the command line.
Of course, there are plenty of other tools around for that kind of task,
including Nmap.
I suspect that Telnet is now mostly used around
stripped-down hardware that's part of research or
development projects of one kind or another.
Someone might, for instance,
be working with a development board for a simplified test prototype that
hasn't got the usual range of physical device interfaces,
like USB.
If the only interface you do have is an old RS-232 Serial Adapter,
then the only way in will probably involve Telnet.
It might also, sometimes,
need to access older hardware or even software environments that
don't support more modern transfer protocols.
Naturally, if you absolutely need to use Telnet over an insecure network,
you can always establish a VPN and operate through that. So it seems the old horse still has some life in it yet.