How to close connections from all IPs, except for selected ones?

Question

iptables

How to close connections from all IPs on VPS (Ubuntu 20.04) except for the ones I need. I tried myself, ended up closing ssh))

Answer 1

We assume that the firewall tables are empty, and there are no rules there.
We allow the necessary addresses:
iptables -A INPUT -i eth0 -p all -s 11.22.33.44 -j ACCEPT
iptables -A INPUT -i eth0 -p all -s 55.66.77.88 -j ACCEPT
now disable everything else
iptables -A INPUT -i eth0 -p all -j REJECT
You can also install ufw and master it, it's a handy and well-documented add-on to iptables