Thanks for your reply. If the first one is so dangerous (Open Resolvers pose a significant threat to the global network infrastructure by answering recursive queries for hosts outside of its domain. They are utilized in DNS Amplification attacks and pose a similar threat as those from Smurf attacks) why is still there? It should be removed!
Lets say I would like to have something more secure than the default settings, are the other two solutions valid? If yes, should I follow both or just one? If instead neither of those is a usefull solution, how do I reset the firewall to default settings? I just select all the rules and then click on the red -? I have a custom port mapping I don’t want to lose with a reset.
Also I have found these:
4) https://rickfreyconsulting.com/basic-mikrotik-firewall-rev-5-0-free-version/
5)http://forum.mikrotik.com/t/trying-to-follow-guide-basic-universal-firewall-script-at-the-wiki/100429/1 (post number 6)
Thanks 