WiFi router & Cable modem question

[John B.]

Qualified answer is “it depends”. Plugging the 2nd WiFi router into the Ethernet port (internal switch port) on your WiFi router puts that 2nd router on your network, not just passing through. If you can configure your main WiFi router to have different network configurations per switch port, you could potentially designate the port the 2nd router is plugged into as a “public Internet” (or similar naming) port, and then it would only allow access upstream to the WAN/cable modem, not to anything else connected to the main router. You could also potentially create a 2nd SSID on the main WiFi router that is “public only”/guest and does the same thing - wireless devices that connect to that SSID would only access the upstream WAN/cable modem. Plus that would eliminate any contention of having 2 wireless routers operating in close proximity.