How to open a port correctly?

Question

linux

I use the site https://portscaner.ru/ to check the opening of ports.
I enter 22 - everything is OK, there is access.
I enter 21 - access is closed. sudo

ufw status

Answer 1

If you have iptables

iptables -I INPUT -p tcp --dport 22 -j ACCEPT
iptables -I INPUT -p tcp --dport 21 -j ACCEPT
service iptables save

If you have a firewall

firewall-cmd --zone=public --add-port=22/tcp   --permanent
firewall-cmd --zone=public --add-port=21/tcp   --permanent

ufw

sudo ufw allow 22/tcp
sudo ufw allow 21/tcp

Also outline your system for accessing the Internet, most likely you are behind NAT and your router sets it.
Therefore, port forwarding needs to be done on the router.
That is, the port is now closed on the router itself, and if you open it, it will be available on the router itself,
respectively, you need to find a place where the following rule is added
22-> 22 tcp 192.168.1.2
something like this
That is, which external port, which it will be a port within the network and, accordingly, to which internal IP to give it.