The Telnet and SSH protocols enable techs to access and control hosts remotely using the command shell in Windows. Telnet offers no security. SSH connections are encrypted for better security.
- I'm old. In fact, I'm so old that I remember using the internet heavily long before there was anything called a World Wide Web or webpages or anything like that. I know it's hard to imagine that, without opening up a browser, you could do anything on the internet. But you could, my friends. And I'm going to show you a couple of those things right now. I want to talk about one of the earliest application protocols ever used on the internet. It's called Telnet. Now, it uses port 23, and to understand Telnet, you have to understand how the internet was back in the old days, before we had things like Windows and pretty MacOSes and stuff like that. What you had is you had operating systems, but all you had was a command line. So, what Telnet did is it allowed me to sit at my computer in my house, but access another computer. But if I was standing in front of that computer, all I'd be seeing is a command line, right? So Telnet simply did that. It was a remote command line tool, and by the way, it still works beautifully today. It's a very, very powerful tool, and it allows me just to get to a command line on some other operating system. Got the idea? Great. Now, in order to access a Telnet server, I have to have a Telnet client. In order to access a web server, you have to have a web browser, right? Well, you'll also have to have a Telnet client, and the Telnet client that's probably the most common and popular is something called PuTTY. In fact, PuTTY has been around for a long time, but it's been constantly updated. It works incredibly well. And if you don't know what PuTTY is, I really don't even consider you a networking person. It's that common of a tool, and it's in every text toolbox. Now, what's cool is that PuTTY is a client for a lot more than just Telnet. In fact, we're going to see a big brother of Telnet called SSH in just a moment, but first, let's use PuTTY to access Telnet. So what I've got here is I've got PuTTY up and running on my computer, and we're about to access a Telnet server that's far away, but I've also got my command line locally open just because I want to run net stats so we can actually see the connection. You ready? Let's do some Telnetting. This is PuTTY over here, and this is the main screen. You'll notice I'm set to Telnet, which is port 23. And all I have to do is type in a fully-qualified domain name, or I could time in a IP address for a Telnet server. So this is the actual name of my Telnet server. So I'm going to hit Open. Now, I'm going to run netstat really quick. Do you see right there? That is the connection that's being made. So my computer is sending out on port 23, and it's going to this computer right here. Okay, so Telnet needs a password to get in. So I'm going to type in a user name, which is going to be mikem, and the password is total. And there's a nice little header, and now I'm actually in the command line, which in this particular case, happens to be a LINUX box, so I'd better type LINUX commands. Or you could be like the guy who set up this Telnet server and has left absolutely nothing in there for me to look at because he's giving me good security. Telnet is fantastic, and it is a great way to access all kinds of stuff. Here, I'm just accessing another computer, but you'll see Telnet being a way to connect to a lot of routers and switches and things like that, but Telnet has one huge problem. It is completely unencrypted. Anybody who's between me and my Telnet server can intercept and read the data, including that user name and password that I typed in? That's all in the clear, and anybody can intercept it and then potentially use it against me. So, it's really important for us to be able to get to other people's command lines, however, I don't want the data between the client and the server to be in the clear. So we're going to stir it up. We're going to mix it up. We're going to encrypt that data, and we're going to do that using Telnet's big brother, SSH. SSH also just gets you to a command line, however, it will be point-to-point encrypted, as we say, and we don't have to do anything. It just automatically encrypts. It's a wonderful, wonderful thing. So let's go ahead and do this all over again, except this time, we're going to use SSH. By the way, SSH uses port 22. So here we are, back to PuTTY again, and I've got my command prompt open here. I'm going to click on SSH in this case. Notice it moves over to port 22. So now I'm going to type in the fully-qualified domain name of my SSH server. And yes, this computer, which is a Telnet server, is also an SSH server. A computer can be more than one kind of server at once. Now, one of the things that's going to happen with SSH is that it's going to send me a key so we can encrypt stuff. So it pops up, it says, do you want to store this key, and we hit yes, otherwise we're not going to be able to work. So I'm going to run netstat -n again, and if you look down here on the bottom, you can see my SSH connection is now connected. So I need to log in, and ta-da! And I guess this one's going to be just as empty as the other. It is. But you've now made a good SSH connection. So, keep in mind, the only times you're going to running Telnet or SSH is because you need to connect to something's command line remotely. So you'll see it in some situations, for example, a lot of routers will allow you to run Telnet or SSH, and a lot of different boxes, more than anything else, will often have Telnet or SSH connections. Now, what's interesting is (laughs) once you get to those command lines, you better know how to run the command line, whether it's LINUX or Mac or Windows or whatever it might be, but at least we can get you there. The last thing I want you to remember about these types of connections is that Telnet is completely unencrypted. So I might use Telnet to connect to a router that's sitting right next to me, but if I need to go to the internet to make any of these types of connections, you will only use SSH. (bouncy music)
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