Check for opened ports without telnet

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If there is no telnet tools is installed on the host, try the following command to check if a port opened or not.

-bash-4.2$ timeout 1 bash -c '(echo > /dev/tcp/ip_adderess/port) >/dev/null 2>&1' && echo Port is open || echo Port is closed

Example

-bash-4.2$ timeout 1 bash -c '(echo > /dev/tcp/192.168.0.100/443) >/dev/null 2>&1' && echo Port is open || echo Port is closed
Port is open

If a port is closed, try to check network configuration or firewall access.