How to check if remote port is open?

Once upon a time I wanted to check if some ports are open. The network I wanted to check was at my office, and when I forwarded some ports on my Mikrotik I wanted to be sure if I did it correctly. So I started to find solution in the internet and I found that netcat can do it:

for localhost:

nc 127.0.0.1 123 < /dev/null; echo $?

for remote host:

nc 194.204.159.1 123< /dev/null; echo $?

After this command you will get an answer 0 or 1.

0 means port is open

1 means port is closed

If you don’t have netcat on your Ubuntu, you can easy install it by command:

sudo apt-get install netcat