How does the repiter mode work on ZYXEL KEENETIC?
Question: Where did the second router come from?
Question #2: Is a USB modem not needed? And it doesn’t need to be bought and inserted into the Zyxel Keenetic Start router?
Answer
I don’t understand what your task is, what you want to do.
You should have a main router that already distributes internet. It doesn’t matter what kind of internet is connected to it, let it be the same USB modem. A router that is configured and gives out internet over wi-fi. And the second router in the repeater mode we configure in order to increase the radius of coverage of Wi-Fi network of the main router. The second router simply acts as an amplifier.
You can’t connect 3G/4G USB-modem to Zyxel Keenetic Start. It does not support them. It doesn’t even have a USB-port. Perhaps you will also find this article on choosing a router that supports USB modems useful.