THE SMART TRICK OF WINBOX THAT NO ONE IS DISCUSSING

/ip firewall filter incorporate chain=enter relationship-condition=recognized,similar motion=accept comment="accept proven,related"; include chain=enter link-state=invalid action=fall; add chain=input in-interface=ether1 protocol=icmp action=accept comment="let ICMP"; include chain=input in-interface=ether1 protocol=tcp port=8291 action=acknowledge