What is telnet command And why is it used here?

why we are using telnet here and what is telnet command ? to check if we can connect to this “devapp01-web server” we can use ping command ?

Hello @gunjanbajaj246,
Ping is an ICMP protocol. Basically, any system with TCP/IP could respond to ICMP calls if they were not blocked by a firewall.
The ping command is used to determine the ability of a user’s computer to reach a destination computer. The main purpose of using this command is to verify if the computer can connect over the network to another computer or network device. It also helps to find out the IP address using the host name:

The telnet command is used for connection and communication with a remote or local host via the Telnet TCP/IP protocol.
You can enter a domain or IP address and try connecting to it via the chosen port. In case the port is not specified, the telnet utility tries to connect via the default port 23.

So here we choose telnet to identify that port(80) is not accessible and the next question will ask you to use ping to check if the machine itself is accessible or not. mainly this will lead to the same result but practicing those commands is an awesome approach for troubleshooting.