The Telnet port - what is it? Connecting and Starting Telnet

Progress is a phenomenon that does not know stops. In the field of information technology, changes occur every day: new products appear, the obsolete services go to the past. But there are tools that are still popular despite the appearance of an alternative. A prime example is the Telnet protocol. What is Telnet and how to use it?

A bit of history: when and why did Telnet appear?

Telnet appeared more than 40 years ago, soon after the installation of the first ARPANET server. This is one of the oldest protocols of the Internet. In an era when the graphic interface was not in sight, and the first networks have already appeared, the need for remote connection to devices dictated their requirements. The first solution to the problem, like all the rest, allowed to work on the remote device as if it were its own. In the command-line interface , all the functionality supported by the remote server became available. It is enough just to get the required level of access and to know the commands of Telnet. What is this protocol for and what we need to understand? But how is Telnet connected today?

Start the terminal. Enable required services

In modern operating systems of the Windows family, before you start Telnet, you need to check whether this component is installed on the system. It is not difficult to do this. For Windows 7, the most common on today's operating system, you need to do the following:

1. Select "Control Panel" or Control Panel in the "Start" menu.
2. In the window that opens, select the "Programs" item. In the English version of the system, this will be Programs.
3. Go to the "Turn Windows features on or off" tab. The system lists all available components. Already installed will be flagged. This process can take a few minutes.
4. After the list is loaded, you need to find the Telnet-client. There is also a Telnet server in the menu, but we will return to this later. If the tick opposite to the item we need is not worth it, you need to put it.
5. After pressing the "OK" button the system will start to set the necessary components for the correct operation of the protocol. It may take some time, but on modern computers the process is unlikely to take more than a minute. Thus, the question of how to enable Telnet was solved in 5 simple steps.

Telnet service: what is a server and a Telnet client?

A little higher, both concepts from the title were already mentioned. Like many other applications, Telnet distinguishes between client and server parts. However, the Telnet server is not necessarily a server in the general sense of the word. The computer from which the connection is made is considered to be the client, the device to which this connection is made will be the server. It can be a router, a computer, a managed switch, or any other host that supports management from the command line. If it is a question of remote administration of a personal computer or server, the Telnet port must be opened. Often, it is closed for security reasons, so when you try to install a session, you will receive an error message. To check open and closed ports, you can use a special utility or web service. The standard Telnet port is 23. If you want to not only connect to other computers on your own, but also allow the administration of your PC via Telnet, then in the same operating system snap-in, you must tick the and opposite the Telnet server component. Similarly, the PCs and server hardware that you are administering must be configured.

Programs for working with Telnet

After running all the necessary Telnet services, you can start work safely with the built-in Windows tool - the command line. It is called from the "Start" menu, either by clicking on the corresponding item, or by quick dialing (cmd). It is always advisable to run a command prompt with the user rights "Administrator" (either local, the device you are working on, or a domain one). In this case, you do not have to restart the application if you need elevation of rights. In addition to the existing operating system tools, there are third-party programs that allow access via the Telnet protocol. The most popular of these is Putty. Along with it, other applications running under different operating systems, such as TeraTerm, AnyConnect, DTelnet, EasyTerm, KoalaTerm and many others are also successful. What program to use, each solves itself, depending on personal preferences, interface requirements, etc. There are no significant differences in terms of functionality between them, and can not be. Each of the utilities implements the entire available list of Telnet commands.

Telnet commands: how to understand?

An experienced network administrator can easily install the necessary components in minutes (if they were not installed earlier), open a Telnet session and perform the entire configuration of the remote host. However, there are newcomers who see the console almost for the first time in their life. How can I find out the list of available commands in Telnet? What is WONT AUTH or SET LOCALECHO? Everything is not as difficult as it seems at first. First, we must always remember that in any command interface there is a built-in help. It can be accessed using standard keys, for example, help or "?". Secondly, considering how old this protocol is, you can find an infinite number of resources on the network with useful information on syntax. Thus, there is absolutely nothing to worry about. And practice shows that using several lines of result commands is much easier to achieve in most cases. And after a few sessions you will confidently dial the necessary commands without accessing the syntax-helper.

Telnet on network devices

We have already said that using Telnet protocol you can manage not only computers, but also various network devices. The most common class of such devices are routers. So what is Telnet in the router, why do we need it, how to enable it?

Depending on the manufacturer and the specific model, you can enable access via Telnet in different ways. You can go to the router through the web interface or through the console. In the first case, you will need to find a remote administration point where this or that type of connection is allowed (Telnet, ssh). In the second case, access can be provided through the command line. Each administrator chooses a script that is convenient for him. However, there are routers in which only one of two possible variants of the initial connection is implemented, for example, only the web interface is available. The administrator, accustomed to working with the console, will be uncomfortable enough to look for the point where you need to put a cherished check, but in reality there is nothing complicated in this. The interface of most modern routers is quite understandable. The names of the menu items speak for themselves, the minimalist design will not allow to get confused.

Advantages of Telnet sessions

By this point, we have sufficiently acquainted with the technology to talk about the advantages and disadvantages of Telnet. No matter how successful the product is, you can not say that it has absolutely no minuses. And if we are talking about a service that was released in the early 70s of the last century, it is not worth forgetting about this fact.

Of the obvious advantages, it is necessary to note the simplicity, speed and convenience of the protocol. In less than a minute, a convenient client will access the TCP port of the server you have selected and create an emulation of the local terminal. Above we talked about the standard 23 working port. In fact, you can "listen" and "talk" through Telnet on any port. This is what the flexibility of the protocol is.

Compared with other remote administration protocols, Telnet is less demanding on the processor. With modern rates of development, this plus may seem insignificant, but only at first glance. Along with the development of technology, companies that produce software do not stand still. Applications are becoming more cumbersome, requiring more space on the hard disk, more RAM, more powerful processors. Utility, which, against the background of the rest of the installed software will consume a small amount of system resources, will have to come in handy.

Disadvantages of the Telnet protocol

The main and often cited drawback of Telnet is that access to the remote device is performed over an unencrypted communication channel. The only obstacle for an attacker is user authentication when the Telnet session is opened, that is, a login and password requirement. However, this data is also transmitted in an unencrypted form. Therefore, if someone wants to hack into Telnet, it's enough to launch packet sniffer for a short time (the software for "catching" packets). After some time, the administrator will open his Telnet session and inform the remote server of the login and password, which will be immediately intercepted by the intruder in the clear. In this section, the alternative to Telnet is the SSH (secure connection). Therefore, it is not recommended to use Telnet in wide access networks, for example, outside your secure local office network. In addition, remember that the connection to the server can be interrupted.

Conclusion. To use or not?

Of course, for more than four decades, there were other ways of remote administration. Great popularity is enjoyed by SSH. It would seem that Telnet should have disappeared for a long time. But it is still in demand, everything is still used. If you follow certain security principles, not forgetting that your local network must be securely protected from outside penetration, using Telnet will not harm your hardware. With a careless attitude to security, neither SSH nor any other technology will save.

Telnet is still used in such areas as connecting to databases, checking the availability of network devices (routers and switches), server hardware, and so on.