Cause: The ONT is actively handling VoIP calls or high throughput. Fix: Unplug the fiber cable (SC/APC) temporarily (just to stop traffic), perform the update, then replug the fiber after reboot.
Before locating the "Update" button, you must understand the stakes. Updating the firmware on an ISP-locked router is different from updating a retail router.
ZTE typically deals directly with ISPs. However, for retail-unlocked units, you can request a file via their regional support email. zte f670l firmware update upd install
Navigate to Diagnosis → Device Info → Hardware Version. Common F670L variants:
Crucial: Firmware for V3.0 will NOT work on V2.0 hardware. Cause: The ONT is actively handling VoIP calls
The ZTE F670L is a GPON ONT/ONU (Optical Network Terminal/Unit) widely used by ISPs (e.g., Claro, Vivo, Telmex, Telenet). Unlike consumer routers, its firmware is heavily ISP-customized. The .upd file is the raw, encrypted binary update package.
The ZTE F670L is not a hobbyist router. It is a carrier-grade GPON terminal. Misguided firmware updates cause three irreversible states: Crucial: Firmware for V3
Call your ISP before updating if: