Telnet is a protocol that allows you to connect to remote computers (called hosts) over a TCP/IP network (such as the internet). Using telnet client software on your computer, you can make a connection to a telnet server (that is, the remote host). Once your telnet client establishes a connection to the remote host, your client becomes a virtual terminal, allowing you to communicate with the remote host from your computer. In most cases, you’ll need to log into the remote host, which requires that you have an account on that system. Occasionally, you can log in as guest or public without having an account.

Telnet clients are available for all major operating systems.

Command-line telnet clients are built into most versions of macOS, Windows, Unix and Linux. To use these clients, go to their respective command lines (that is, the Terminal application in macOS, the Shell in Unix or Linux, or the DOS prompt in Windows), and then enter:

What type of protocol is Telnet?

Telnet is a client–server protocol, based on a reliable connection-oriented transport. Typically, this protocol is used to establish a connection to Transmission Control Protocol (TCP) port number 23, where a Telnet server application (telnetd) is listening.

For example, typing telnet hostname would connect a user to a hostname named hostname. Telnet enables a user to manage an account or device remotely. For example, a user may telnet into a computer that hosts their website to manage his or her files remotely. … As shown, a telnet session is a command line interface.

What is Telnet used for?

Telnet, developed in 1969, is a protocol that provides a command line interface for communication with a remote device or server, sometimes employed for remote management but also for initial device setup like network hardware.

WHAT IS A SWITCH

A switch is a device in a computer network that connects other devices together. Multiple data cables are plugged into a switch to enable communication between different networked devices. … A device that also operates at these higher layers is known as a multilayer switch.

What are switches used for in networking?

Switches facilitate the sharing of resources by connecting together all the devices, including computers, printers, and servers, in a small business network. Thanks to the switch, these connected devices can share information and talk to each other, regardless of where they are in a building or on a campus.

Types of Switches

Modular switches vs. fixed-configuration switches

There are two main categories of switches: modular and fixed configuration. There are variations among these categories of network switches, but the primary definition of each remains the same. 

Modular switches

Modular switches let you add expansion modules as needed, giving you flexibility as network requirements change. Expansion modules are application-specific and include those for firewalls, wireless connectivity, or network analysis. They may also allow for additional interfaces, power supplies, or cooling fans. This type of switch provides you with the most flexibility, but at a higher cost. 

Fixed-configuration switches

Fixed-configuration switches provide a fixed number of ports and are typically not expandable, which makes them less expensive overall. Fixed-configuration switches include unmanaged switches, smart switches, and managed switches.

Unmanaged switches

Unmanaged switches are typically used to provide basic connectivity. They’re designed to be plug and play; no configuration is needed. Unmanaged switches are most effective when only basic switching and connectivity are required. You will often see them in home networks or wherever only a few ports are needed, such as at a desk, in a lab, or in a conference room. 

Some unmanaged switches do offer limited advanced capabilities, however—as the name implies—these switches generally cannot be modified or managed.  

Smart switches

Smart switches offer some management and segmentation, quality of service, and security capabilities, so they can be a cost-effective alternative to modular switches. Still, they are not as scalable as managed switches. These switches are typically deployed at the edge of a large network (while managed switches are used in the core), as the infrastructure for smaller networks, or for low complexity networks. 

Managed switches

Among fixed-configuration switches, managed switches are designed to deliver the most comprehensive set of features to provide the best application experience, the highest levels of security, the most precise control and management of the network, and the greatest scalability. As a result, managed switches are usually deployed as aggregation/access switches in very large networks or as core switches in smaller networks. 

Managed switches are the most expensive option of fixed-configuration switches and are most common in organizations with large- or growing- networks.

Feature Options

Four switch options to keep in mind

In addition to evaluating switch categories, you should also consider network switch speeds, number of ports, power-over-Ethernet features, and stacking capabilities.

1. Switch speeds
   Switches are available in different throughputs or speeds, the rate they transmit data in megabits per second (Mbps). For example, fixed-configuration switches can provide Fast Ethernet (10/100 Mbps), Gigabit Ethernet (10/100/1000 Mbps), Ten Gigabit (10/100/1000/10000 Mbps), and even 40/100 Gbps (gigabits per second) speeds. The switch speed you choose depends on the type of throughput you need. If, for example, you need to move large data files on a regular basis, you should consider a Gigabit Ethernet switch.
2. Number of ports
   As is the case with switch speed, the number of ports available in a switch can vary. The bigger your small business and the more network users you have, the more ports you’ll need. Fixed-configuration switches are usually available with five, eight, 10, 16, 24, 28, 48, or 52 ports.
3. Power over Ethernet (PoE) vs. non-PoE
   PoE lets you power a device—such as an IP phone, surveillance camera, or wireless access point—over the cable that is used for data traffic. This allows you to place endpoints anywhere, even in those areas that are usually difficult to reach. Switches with PoE are more expensive, however. As you evaluate your options, think about the devices you would like to connect to determine whether PoE is required.
4. Stackable vs. standalone switches
   As your business (and your network) grows, you will likely need to support more and more devices, which will mean investing in more switches. Just as its name implies, a standalone switch is managed and configured as an individual entity with limited capacity. If there is a problem, troubleshooting is also switch specific.

In contrast, stackable switches can be connected to increase the capacity and availability of your network. Rather than configuring, managing, and troubleshooting each switch, you can treat the “stack” as a single unit. This means that if any part of the stack fails, the stack will route around the failure, so your network keeps running.

HOW TO CONFIGURE TELNET IN CISCO SWITCH

First of all, we will check our interface IPs by running show ip interface brief and choose an interface for telnet.

Cisco-RTR#show ip interface brief
Interface                  IP-Address      OK? Method Status                Protocol
GigabitEthernet0/0         10.1.1.50       YES NVRAM  up                    up      
GigabitEthernet0/1         172.16.0.1      YES NVRAM  up                    up      
GigabitEthernet0/2         172.16.1.1      YES NVRAM  up                    up      
GigabitEthernet0/3         unassigned      YES NVRAM  administratively down down    
GigabitEthernet0/4         unassigned      YES NVRAM  administratively down down    

You can see interface gig0/0 to gig0/2 has IP addresses. And, we can telnet any IPs of this list, as long as we have the reachability. In this example, we will telnet on 10.1.1.50.

Telnet configuration will be in the bottom of the configuration file. You can use show run command to see the configuration. You also can use filter commands to go telnet configuration directly run using show run | section vty.

Cisco-RTR#show running-config | section vty
line vty 0 4
 login
 transport input none

VTY is a virtual port that helps to get Telnet or SSH access to the device. And, we will enable our telnet under line vty.

Before enabling telnet, you should know, we can enable telnet in two ways. In the first way, we will add a password for telnet. By this way, whenever someone tried to telnet to the device, they only need to use password, no username. Problem with this method is, you will not be able to identify who joined to the telnet session.

In the 2nd way, we can enable telnet for local users, where a telnet user need to have an account on the device.

Let’s configure telnet in first ways.

Method 1:

Cisco-RTR#configure terminal
Cisco-RTR(config)#line vty 0 4
Cisco-RTR(config-line)#transport input telnet 
Cisco-RTR(config-line)#password cisco
Cisco-RTR(config-line)#login

Explanation:
transport input telnet: Enabling telnet.
password cisco: Setting the password for telnet. Password is cisco.
login: Allowing login

That’s it for 1st way. Now we can test our configuration. Let’s open a putty session and try to telnet 10.1.1.50.

As expected, it is asking the password. After using password cisco and we are successfully logged in.

Now, let’s identify the problem with this method. We will run show users command.

You can see, two people are logged in, one is using console and one is in vty. But, you will not be able to identify who logged in using vty.

Now, let’s move to the 2nd method.

Method 2:

Below are our configuration-

Cisco-RTR#configure terminal
Cisco-RTR(config)#line vty 0 4
Cisco-RTR(config-line)#transport input telnet 
Cisco-RTR(config-line)#login local

Explanation:
transport input telnet: Enabling telnet.
login local: Allowing login using local credentials.

Now, we will test our telnet configuration by doing the telnet to the device. Let’s telnet to 10.1.1.50.

You can see it’s asking username, let’s use username rajib and then use its associated password.

Now, let’s check who is logged in to the device by running show users command.

You can see, in vty session user rajib is logged in. Due to this, method 2 is more preferred than method 1.

You also can watch how to enable telnet on Cisco in my YouTube channel.https://www.youtube.com/embed/9uZ3DcJth9g?autohide=2&autoplay=0&mute=0&controls=1&fs=1&loop=0&modestbranding=0&playlist=&rel=1&showinfo=1&theme=dark&wmode=&playsinline=0

This is how to configure Telnet on Cisco IOS routers and switches. Hope you will enjoy. Let me know if you have any questions about Telnet configuration.

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