@Sunshine 

The SPI firewall is what I am using now as it is the only option I have without additional hardware.

What I would like to do is to use two routers with a single incoming internet connection to handle two separate networks.  The problem arises when there is a need to communicate from one network to the other.  The SPI firewall blocks all incoming connections and there is no way to selectively allow incoming traffic from a known source.  Disabling the SPI firewall allows traffic to pass through but also leaves the routers with no protection.  The capability to specify additional rules would solve this problem.

  @Sunshine 

In my earlier response to you, I did not explain much in detail the reasoning for the feature request.  What I mentioned is only the beginning as my network continues to grow.

I, like many other experienced computer users, do not want to rely on phone apps (such as Tether, and cloud-based services (such as HomeShield) to manage my router(s).  These may be selling points for the vendor and hence, the reason for reluctance to implement features like firewall rules.  In looking at similar routers by other manufacturers, such as D-Link and Keenetic, the ability to create and manage firewall rules for allowing, denying, or restricting traffic in both directions is a plus for them.  The inexpensive D-Link Eagle Pro AI AX1500 R15 router is one example where the user can have up to 24 rules.  Even my ISP’s router (made by Mitrastar) has a rule capability for both the WAN and LAN ports.

Myself, and many others, surely would appreciate the capability to set up rules where we could specify in each rule the:
1) WAN or LAN for incoming packets
2) Source IP address/range
3) Destination IP address/range
4) Protocol and port range
5) Schedule

Hopefully, Top-Link can provide this capability in the near future, making them stand out from the others, just like they are doing now with the implementation of separate IoT networks.