A bit of theory: setting up a firewall
One of the basic concepts for setting up a Mikrotik firewall is a chain. There are 3 by default, but it is possible to create your own chains:
- The INPUT chain is the incoming traffic coming to the router.
- The OUTPUT chain is the outgoing traffic generated by the router.
https://telegra.ph/Nastrojka-Firewall-v-Mikrotik-09-28