Telnet

Telnet is a application layer protocol where one system can access and use another system over a virtual connection using Telnet Client and Telnet Server by logged into a user's account on port number 23, if they are connected locally.

How telnet works:

Step 1) Install Telnet Client and Telnet server at both client and server side

Step 2) Create a account (Username and password) in client side.

Step 3) Telnet client will send a request to Telnet Server.

Step 4) Telnet server will reply back with asking username and password.

Step 5) If accepted, Telnet Client will established a connection with client.

Step 6) Via virtual terminal, we have access to the client's system.

This all happen when client initiates TCP 3 way-handshake to the server.

Let's see how it does look like, we'll use wireshark for instance.

TCP Handshake before Telent:

Telnet Server IP: 192.168.0.1
Telnet Client IP:  192.168.0.2

 Telnet Server ask for login details to Telnet Client:

Telnet Client response with credentials:

UserID:

Password:

 And Finally Session is closed: