[Mashiro]

iptables is always the same regardless of the Linux distribution used. ufw is a frontend to make iptables usage easier.

The rules that you used from the guide are either wrong (as in misconfigured) or you trigger the block when you connect to the server and get kicked off by the firewall.

You can't stop DDoS using just iptables. DDoS originates from multiple sources and a lot of attackers. All of these articles claiming that you can use iptables on the same machine to stop DDoS attacks are misleading and wrong! You can stop attacks from single attackers (that is DoS not DDoS) by blocking them with iptables, though.