Search for “Huawei B311221 Unlock Firmware Top 2024/2025” on reputable forums (4PDA, XDA, Huawei-Mods). Look for files with high download counts and positive feedback. Ensure the file is for B311221, not B311s-936 (though compatible, check notes).
Solution: Some carriers store the SIM lock in a separate NVRAM partition. After flashing the top unlock firmware, you still need to run a "Factory Unlock" command via AT. In the router's debug page (http://192.168.1.1/html/debug.html), send: AT^CARDLOCK="unlock_code". If you don’t have the code, use DC-Unlocker. huawei b311221 unlock firmware top
Solution: The firmware might be semi-unlocked. You need to enable "Engineering mode permanently." Send the AT command: AT^SFM=1 over Telnet (port 23). Then reboot. not B311s-936 (though compatible