Telnet is a network protocol that allows a user to communicate with a remote device. It is a virtual terminal protocol which network administrators use widely to remotely access and manage devices. Administrator can access the device by telnetting to the IP address or hostname of a remote device.
To use it, you must have a software (Telnet client) installed. On a remote device, a Telnet server must be installed and running. This protocol uses the TCP port 23 by default.
There is one very big disadvantage of this protocol. The issue is that all data, including usernames and passwords, is sent in clear text, which therefore becomes a potential security risk. This is the main reason why this protocol is rarely in use today and many of us are planning to replace it by a much secure protocol called SSH.
The word telnet can also refer to the software that implements the this protocol.
On Windows, you can start a session by just typing the telnet IP_ADDRESS or HOSTNAME command:
SSH (Secure Shell)
It is a network protocol that we use to remotely access and manage a device. The key difference between Telnet and SSH is that SSH uses encryption. This means that all data transmitted over a network is also secure from eavesdropping. It uses the public key encryption for such purposes.
Like Telnet, a user accessing a remote device must have an SSH client installed. On a remote device, an SSH server must be there and running. It uses the TCP port 22 by default.
There is also an example of creating an Secure shell session using Putty, a free SSH client:
SSH is the most common way to remotely access and manage a Cisco device.
In case you have any queries, please feel free to post them in the comments section below.