If you are a of this ONT/ONU device (commonly used in fiber optic networks from ISPs like Movistar, Telmex, Claro, etc.) and have lost access, here is general information:
Here's a feature of the ZTE F663NV3A:
The device, which looked like a small white box with blinking lights, was a mystery to them. They had heard that it was a gateway to the world of high-speed internet, but they didn't know much about it. password zte f663nv3a exclusive
You can restore the unit to its original settings by holding the Reset button (using a pin) for about 10–15 seconds while the device is powered on. Warning: This will erase all custom settings, including your internet connection configuration (PPPoE/VLAN tags), which you may need to re-enter manually. Managing Your Security If you are a of this ONT/ONU device