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Telnet is one of the most used protocols by network engineers. It is basically used to connect a network device remotely. In this lesson, we will learn the details of this important protocol in networking. Another important protocol that we use for remote access is SSH (Secure Shell). We have talked about SSH in related lesson. Now, we will focus on Telnet protocol. So, let’s start with what is telnet.
Table of Contents
Telnet is a network protocol which provides remote access to the network devices. It is the abbreviation of “Telecommunications Network”. It is a standard of ISO (International Organization for Standardization). Telnt, uses TCP protocol as transport protocol. And TCP port 23 is the default telnet port.
Telnet is a Client-Server protocol. One of the sides which use this protocol is server and the other side is client. The main role of this protocol is connecting the remote server and opening command line interface (CLI) on this server. This command line is used by client.
Telnt is an old network protocol. It is used since 1960s in ARPANET (Advanced Research Projects Agency Network). After that network engineers has used this protocol and at 1973 it is documented. At 1983 this protocol became a standard with as RFC 854.
Telnett was operating over Network Control Protocol also known as Teletype Over Network Protocol. Firstly, it was using 8-bit channel for transmission but in time it has developed.
As we mentioned before, it is a Client-Server protocol. Here, client side connects server side and opens a command line interface on this server. After this connection, user can do anything on this server over CLI. Your client device can be a PC and the server side can be a router or a switch. With this telneet connection, you can connect your router or switch and then you can configure is as you are directly connected.
Tellnet uses plain-text between this client and server. So, this makes this communication unsecure. It uses American Standard Code for Information Interchange (ASCII).
We can access a device with “telnet” keyword and the ip address of the remote device to conenct that remote device.
Telnet is not a secure network protocol. Because the packets of this protocol is not encrypted. They are sent as plain-text. This means that, anyone can see your credentials like; usernames, passwords or any other critical information. So, it is is vulnerable to network attacks.
The main usage of telnet is network device management. Network engineers manage network devices like routers, switches, firewalls etc. remotely with this protocol. During integration, maintenance or upgrade, this protocol is an important protocol. But today, it is mainly replaced with SSH.
Beside telnnet is used for troubleshooting activities. With this protocol, you can check the availability of the devices in the network.
Telnet protocol has different advantages and disadvantages. Let’s start with the advantages.
With this remote access protocol, you can easily access any device on a remote site. So, tlnet provides remote access. It is a quick way to connect a network device. So, it saves operation time. These are the advantages of this remote access protocol.
What about disadvantages? First of all, the data is sent in plain-text with this protocol. This means that there is no encryption in telnet. So, it is not a secure protocol.
Telnet is replaced with SSH (Secure Socket Shell). So, we can do anything with SSH that with do with Tlnet. Beside SSH is more secure.
SSH is also more functional than Telnet. With SSH, we can use tunneling and file transfer opportunities also.
Lastly, telnet is used in local networks. Because it is more secure than outside. But SSH is mostly used on public networks.
Taking all things into account, today, instead of Telnnet, SSH is preferred.
To use Telnet on Cisco devices, we should configure Telenet on that device. To configure telnet on Cisco routers or switches, we need to follow some steps.
Here, firstly, we enter 16 telnet sessions from 0 to 15 with “line vty 0 15” command, then we determine a password with “password password” command. Here, our password will be cisco123. Then, to enable remote login, we will use “login” command.
Router (config)# line vty 0 15
Router (config-line)# password cisco123
Router (config-line)# login
To connect to a device with this protocol we use “telnet ip-address” command.
For IPv4 and IPv6 Telnet configuration examples, you can visit related lesson.
The default telnet port is TCP port 23.
Today, Telnet is replaced with SSH (Secure Socket Shell). SSH is more secure. It uses encryption for the data. Beside SSH offers extra properties like tunneling and file transfer. So today, mostly, SSH is used instead of Telnett.
Telnet uses American Standard Code for Information Interchange (ASCII).
The default SSH port is TCP port 22.
SSH is the abbreviation of Secure Shell.
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