Progress is a phenomenon that does not know stops. In the field of information technology, changes occur every day: new products appear, outdated services become obsolete. But there are tools that are still popular despite the emerging 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, shortly after installing the first ARPANET server. This is one of the oldest Internet protocols. In an era when there was no graphical interface at all, and the first networks had already appeared, the need for remote connection to devices dictated its own requirements. The first solution to the emerging problem, like all subsequent ones, made it possible to work on the remote device as if it were ours. In the command line interface , all the functionality supported by the remote server has become available . All you need is to get the required access level and know the Telnet commands. What is and why this protocol is needed we figured out. But how is Telnet connected today?
Launch terminal. Enabling required services
In modern operating systems of the Windows family, before starting Telnet, it is necessary to check whether this component is installed on the system. Make it easy. For Windows 7, the most common operating system to date, you must follow the steps below:
- Select "Control Panel" or Control Panel in the "Start" menu (Start).
- In the window that opens, select the "Programs" item. In the English version of the system, this will be Programs.
- Go to the tab "Turn Windows features on or off" (Turn Windows features on or off). The system compiles a list of all available components. Already installed ones will be marked with flags. This process may take several minutes.
- After the list is loaded, you need to find the Telnet client item. There is also a Telnet server in the menu, but we will return to this a bit later. If the check mark opposite the item we need is not worth it, you need to put it.
- After clicking "OK", the system will begin to install the necessary components for the correct operation of the protocol. This 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 resolved in 5 simple steps.
Telnet Service: What is a Telnet Server and Client?
Both concepts from the heading have already been mentioned a little higher. 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 command-line management. If we are talking about remote administration of a personal user computer or server, the Telnet port should be open. Often it is closed for security reasons, so when you try to establish a session, an error message appears. To check open and closed ports, you can use a special utility or a web service. The standard Telnet port is 23. If you want to not only independently connect to other computers, but also allow administration of your PC via Telnet, then in the same snap-in of the operating system you need to check the box next to the Telnet server component. Similarly, the PCs and server hardware that you administer should be configured.
Programs for working with Telnet
After starting all the necessary Telnet services, you can safely start using the built-in Windows tool - the command line. It is called from the Start menu, either by clicking on the corresponding item, or by speed dialing (cmd). It is advisable to always run the command line with the Administrator user rights (either local, the device on which you are working, or domain). In this case, you do not have to restart the application if you need to elevate the rights. In addition to the existing tool of the operating system itself, 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. Everyone decides which program to use, depending on personal preferences, interface requirements, etc. There are no significant differences in terms of functionality between them, and there cannot be. Each of the utilities implements the entire available list of Telnet commands.
Telnet commands: how to figure it out?
It will not be difficult for an experienced network administrator to install the necessary components in a matter of minutes (if they have not been previously installed), open a Telnet session and complete the entire remote host configuration. However, there are beginners who see the console almost the first time in their lives. How to find a list of available commands in Telnet? What is WONT AUTH or SET LOCALECHO? Everything is not as complicated as it seems at first. First, you should always remember that any command interface has 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 syntax information. Thus, there is absolutely nothing to worry about. But practice shows that with a few lines of commands the result is much easier to achieve in most cases. And in just a few sessions, you will confidently type the necessary commands without accessing the syntax assistant.
Telnet on network devices
We have already said that using the Telnet protocol, you can control not only computers, but also a wide variety of network devices. The most common class of such devices is routers. So what is Telnet in the router, why is it needed, how to enable it?
Depending on the manufacturer and the specific model, you can enable Telnet access in different ways. You can access the router via the web interface or through the console. In the first case, you will need to find a remote administration point where one or another type of connection is allowed (Telnet, ssh). In the second case, access can be granted via the command line. Each administrator chooses a convenient scenario. However, there are routers in which only one of the two possible options for the initial connection is implemented, for example, only the web interface is available. An administrator who is used to working with the console will be rather uncomfortable looking for a point where you need to put a treasured checkmark, but in reality there is nothing complicated about it. The interface of most modern routers is quite clear. The names of the menu items speak for themselves, the minimalist design will not let you get confused.
Benefits of Telnet Sessions
At this point, we have become sufficiently familiar with the technology to talk about the pros and cons of Telnet. No matter how successful the product may be, it cannot be said that it is completely devoid of cons. And if we are talking about a service that was released at the very beginning of the 70s of the last century, you should not forget about this fact at all.
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 server’s TCP port of your choice and create an emulation of the local terminal. Above we talked about the standard 23 working port. In fact, you can "listen" and "talk" on Telnet on any port. This is where the flexibility of the protocol lies.
Compared to other remote administration protocols, Telnet is less CPU intensive. With the current pace of development, this plus may seem insignificant, but only at first glance. Along with the development of technology, companies that release software do not stand still. Applications are becoming more cumbersome, require more space on your hard drive, more RAM, more powerful processors. A utility that, against the background of the rest of the installed software, will consume a small amount of system resources, will come in handy.
Disadvantages of Telnet Protocol
The main and often cited drawback of Telnet is that access to the remote device is via an unencrypted communication channel. The only obstacle for the attacker is user authentication at the time of opening the Telnet session, that is, the requirement for a login and password. However, this data is also transmitted in unencrypted form. Therefore, if someone wants to hack Telnet access, it is enough for him to run packet sniffer (software for "catching" packets) for a short while. After some time, the administrator will open his Telnet session and inform the remote server of the username and password, which will be immediately intercepted by the attacker in clear form. In this context, an alternative to Telnet is SSH (secure connection). Therefore, it is not recommended to use Telnet in widely available networks, for example, outside your secure office LAN. In addition, it should be remembered that the connection to the server may be interrupted.
Conclusion Use or not?
Of course, over more than four decades, other methods of remote administration have appeared. SSH is very popular. It would seem that Telnet should have disappeared a long time ago. But it is still in demand, it is still used. If you follow certain security principles, not forgetting that your local network must be reliably protected from outside penetration, using Telnet will not harm your equipment. With a negligent attitude to security, neither SSH nor any other technology will save.
Telnet is still used in areas such as connecting to databases, checking the availability of network devices (routers and switches), server hardware, etc.