WHAT IS TELNET, SSH (Secure Shell) , NETWORK PORT

 

Telnet

Telnet is a network protocol that allows you to connect to remote hosts on the Internet or on a local network. It requires a telnet client software to implement the protocol using which the connection is established with the remote computer.

In most cases telnet requires you to have a username and a password to establish

connection with the remote host. Occasionally, some hosts also allow users to make connection as a guest or public.

After the connection is made, one can use text based commands to communicate with the
remote host. The syntax for using the telnet command is as follows:

telnet <hostname or IP> port

Example:telnet 127.0.0.1 25

SSH (Secure Shell)

SSH is a protocol similar to telnet which also facilitates connection to remote hosts for communication. However, SSH has an upper hand over telnet in terms of security. Telnet was primarily designed to operate within the local network and hence does not take care of security. On the other hand SSH manages to offer total security while connecting to remote hosts on a remote network or Internet.

Akin to telnet SSH also uses a client software and requires a username and password to establish connection with the remote host.

NETWORK PORT

A computer may be running several services on it like HTTP (web server), SMTP, FTP and so on. Each of these services are uniquely identified by a number called network port (or simply referred to as port). If a computer wants to avail a specific service from another computer, it has to establish a connection to it on the exact port number where the intended service is running.

For example, if a terminal is to request a web document from a remote server using HTTP, it has to first establish a connection with the remote server on port 80 (HTTP service runs on port 80) before placing the request.

In simple words, port numbers can be compared to door numbers where each door grants access to a specific service on a computer. The following table shows a list of popular services and their default port numbers: