当大多数人想到 Internet 时，他们真正想到的是Web。然而，构成互联网的物理网络承载的不仅仅是网站和我们每天都在使用的面向公众的服务。
事实上，大多数(most )互联网根本与网络无关，而是大量使用各种“协议(protocols)”的其他互联网服务。例如， HTTP 或超文本传输协议(hypertext transfer protocol )用于为您的浏览器提供网站服务。Telnet也是一种互联网协议，但它具有不同的历史和一些有趣的用途。
但是什么是远程登录？在本文中，您将了解到这一点。
什么是 Telnet？
Tim Starling (WMF) / CC BY-SA (https://creativecommons.org/licenses/by-sa/4.0)
Telnet是一种基于文本的网络协议，它允许客户端（即您）与互联网上某处的远程计算机进行通信。通常，Telnet连接通过端口(Port)23 运行，并且与网站一样，Telnet服务具有特定地址。
过去，您可能使用专用终端来访问Telnet服务。终端并不是真正完整的计算机，而只是为远程计算机提供远程“面孔”的设备。
如今，从智能手表(smartwatch)到智能电视(smart TV)，几乎所有东西都具有完整的计算能力，因此哑终端不再真正得到太多使用。为了今天使用Telnet服务，您需要一个称为终端仿真器(terminal emulator)的应用程序。好消息是每个操作系统都有一大堆很棒的免费终端模拟器。(great free terminal emulators)
您可能会认为Telnet听起来不再那么重要了。虽然它是一种比较不起眼的互联网服务，但在全球范围内有一个规模庞大且专门的Telnet社区。
它在低带宽远程计算机管理中仍然具有非常重要的作用。这意味着Telnet不仅远未消亡，它还有一个光明的未来。然而，在我们开始之前，让我们快速了解一下Telnet的来源。
Telnet 简史
Erik Pitti / CC BY (https://creativecommons.org/licenses/by/2.0)
在今天的互联网之前，有阿帕(ARPANET)网。一个军事和学术计算机网络，当时只有拥有计算机的人为政府机构或机构工作。有问题的计算机是填满整个房间的大型机器。这是在个人电脑的想法出现在任何人的脑海中之前。
让计算机通过这个新网络相互通信并非易事。主要是因为这些机器各自具有非常不同的设计和架构。
我们需要的是一种单一的共享语言。1971 年，起草了Telnet协议的第一个提案。(Telnet)然而， Telnet(Telnet)本身需要十多年的时间才能作为一种工作技术发布。1983 年，第一个 telnet 协议迭代发布。
Telnet 作为远程管理工具
Telnet 可用于向远程系统发送命令，因此可以通过终端接口控制它们。现在很少这样做了，SSH（安全外壳(Secure Shell)）协议主要取代了Telnet的目的和功能。
但是，Telnet仍然很重要，因为运行以前时代的操作系统但今天仍在使用的系统可能只能通过Telnet访问。某些互联网设备，例如某些路由器，也可能只响应Telnet命令。
这实际上是Telnet的主要优势之一。这是一个如此古老和基础的协议，通常可以依靠它来可靠和一致地工作。毕竟，它的目的是成为计算机发送和接收命令的通用语言。但是，如果可能的话，它不应该被用作一线技术。Secure Shell通常是几乎所有情况下的最佳选择，
什么是 Telnet 与安全外壳
Telnet是在没有人真正想到网络安全的时候开发的。由于只有受信任的参与者拥有具有网络访问权限的计算机，因此有人会入侵计算机的想法非常牵强。
今天，数十亿人拥有一台电脑和互联网连接。黑客(Hackers)不断地攻击远程系统，这意味着他们一直在寻找新的漏洞。由于Telnet以纯文本形式发送命令，并且每个人都知道它默认使用哪个网络端口，因此拦截或修改数据相当简单。
Secure Shell通过对其发送和接收的所有数据使用强加密解决了这个问题。这是它取代Telnet(Telnet)的主要原因之一。话虽如此，现在还有一些方法可以对Telnet应用加密，尽管它不是协议的集成部分
如何访问 Telnet 服务
要连接到Telnet服务，您只需要一个终端仿真器和您要连接的计算机的地址。
有很多终端模拟器。其中大部分是免费的。在这种情况下，我们将使用流行的Tera Term。作为演示，我们将连接到一个Telnet服务，该服务使用ASCII文本来复述整个第一部星球大战(Wars)电影。
通常，对于传统的终端应用程序，您会键入“telnet”，后跟一个空格和服务地址。您可能还必须在命令中指定端口，通常是Telnet的端口 23 。但是，Tera Term有一个图形界面，所以我们所要做的就是像这样填充屏幕。
如您所知，此服务的地址是 towel.blinkenlights.nl。如上所述配置所有内容后，只需单击“确定(OK)”即可。
惊人的！对？让我们不要停止那里的乐趣。这里有更多 Telnet 服务，您可以在使用该终端应用程序时使用。
酷 Telnet 服务
既然我们已经介绍了有关Telnet的基本事实，没有比为您指出一些您现在可以访问的有趣地方的方向更好的方法来完成这个速成课程了。
Telnet.org维护着一个庞大的Telnet访问地点列表。你应该去那里寻找更晦涩的目的地，但这里是大多数人会从中获得乐趣的亮点：
从这里你是你自己的。但是如果你有耐心，Telnet的世界会非常值得探索和试验。您很快就会在ASCII中做梦！
HDG Explains: What Is Telnet?
When most people think of the internet, what they’re really thinking of is the Web. However the physiсal netwоrk that makes up the internet carries far more than just websites and the public-facing serviceѕ we all use every day.
In fact, most of the internet isn’t related to the web at all, but rather a whole slew of other internet services that use various “protocols”. HTTP or hypertext transfer protocol is used to serve websites to your browser, as one example. Telnet is also an internet protocol, but one with a different history and some interesting uses.
But what is telnet? In this article you’ll learn just that.
What Is Telnet?
Tim Starling (WMF) / CC BY-SA (https://creativecommons.org/licenses/by-sa/4.0)
Telnet is a text-based network protocol that lets a client (that’s you) communicate with a remote computer, somewhere out there on the internet. Usually, Telnet connections run over Port 23 and, just like websites, Telnet services have a specific address.
In the past, you may have used a dedicated terminal to access a Telnet service. Terminals aren’t really full computers, but simply devices that provide a remote “face” for a distant computer.
These days, just about everything from a smartwatch to a smart TV has full computing power, so dumb terminals don’t really get much use anymore. In order to use a Telnet service today, you’ll need an application known as a terminal emulator. The good news is that there are a whole bunch of great free terminal emulators out there for every operating system.
You might be thinking that Telnet doesn’t sound all that relevant anymore. While it is a more obscure internet service, there’s a sizable and dedicated Telnet community worldwide.
It also still has a very important role in low-bandwidth remote computer management. Which means that not only is Telnet far from dead, it still has a bright future ahead of it. Before we get to that, however, let’s take a quick look at where Telnet came from.
A Brief History Of Telnet
Erik Pitti / CC BY (https://creativecommons.org/licenses/by/2.0)
Before the internet of today, there was ARPANET. A military and academic computer network at a time when the only people who had computers worked for government agencies or institutions. The computers in question were massive machines that filled entire rooms. This was before the idea of a personal computer was on anyone’s mind.
Getting computers to talk to each other over this new network was no easy task. Mainly because these machines each had very different designs and architectures from one another.
What was needed is a single shared language. In 1971, the first proposal for the Telnet protocol was drafted. However, It would take more than a decade for Telnet itself to be released as a working technology. In 1983, the very first iteration of telnet protocol was released to the world.
Telnet As A Remote Management Tool
Telnet can be used to send commands to remote systems and therefore control them through the terminal interface. This is rarely done these days, with the SSH (Secure Shell) protocol mostly replacing the purpose and function of Telnet.
However, Telnet is still important, because systems that run operating systems from previous eras, but are still in use today, might only be accessible through Telnet. Some internet appliances, such as certain routers, might also only respond to Telnet commands.
That’s actually one of the key advantages of Telnet. It’s such an old and fundamental protocol that it can often be relied upon to work reliably and consistently. After all, it’s purpose was to be a universal language for computers to send and receive commands. However, it should not be used as a first-line technology if at all possible. Secure Shell is generally the best choice in almost every situation,
What Is Telnet vs Secure Shell
Telnet was developed at a time when the idea of cyber security wasn’t really on anyone’s mind. Since only trusted actors had computers with network access, the idea that someone would hack into a computer was pretty far-fetched.
Today billions of people have a computer as well as an internet connection. Hackers are constantly attacking remote systems, which means that they are always looking for a new vulnerability. Since Telnet sends its commands in plain text and everyone knows which network port it uses by default, it’s fairly trivial to intercept or modify the data.
Secure Shell solves this issue by using strong encryption on all the data it sends and receives. This is one of the main reasons it has supplanted Telnet. That being said, these days there are also ways of applying encryption to Telnet, though it’s not an integrated part of the protocol
How To Access A Telnet Service
To connect to a Telnet service, all you need is a terminal emulator and the address of the computer you want to connect to.
There are plenty of terminal emulators. Most of them are free. In this case we’re going to use the popular Tera Term. As a demonstration, we’ll connect to a Telnet service that uses ASCII text to retell the entire first Star Wars film.
Usually, with a traditional terminal application you’d type “telnet” followed by a space and the address of the service. You may also have to specify the port in the command, which is usually port 23 for Telnet. However, Tera Term has a graphical interface, so all we have to do is fill in the screen like so.
As you can tell, the address for this service is towel.blinkenlights.nl. With everything configured as above, just click OK and this happens.
Awesome! Right? Let’s not stop the fun there. Here are some more Telnet services you can play around with while you have that terminal app out.
Cool Telnet Services
Now that we’ve covered the essential facts about Telnet, there’s no better way to round off this crash course than to point you in the direction of some interesting places you can visit right now.
Telnet.org maintains a huge list of Telnet places to visit. You should head over there to get the more obscure destinations, but here are the highlights most people will get a kick out of:
From here you’re on your own. But if you’ve the patience, the world of Telnet can be pretty rewarding to explore and experiment with. You’ll be dreaming in ASCII in no time!
