Notes

Adding this rule to the AZTCO-FW firewall will block access to bridge devices like cable modems or upstream routers outside of the WAN interface. For example, many cable modems use an IP address of 192.168.100.1. This may or may not be desirable behavior for users. The RFC1918 firewall rule needs to be disabled if access from inside the LAN to a device like this is required.

On the edit interfaces screen (Interfaces > WAN, for example) there is an option to Block private networks. This is a rule blocking inbound traffic, not outbound like the rule described here. As long as the AZTCO-FW instance is not behind a WAN that uses private addressing, both rules are desirable and should be enabled.