A basic firewall to protect router itself and clients behind the router, for both IPv4

IPv4 firewall 

Protect the router itself

Rules of thumb followed to set up the firewall:

• work with new connections to decrease the load on a router;
• accept what you need
• drop everything else, log=yes could be set to log some attackers, but keep in mind that it may add some load to he CPU on heavy attacks.

We always start by accepting already known and accepted connections, so the first rule should be to accept "established" and "related" connections.