[Redmi Note 11 (spes/spesn)] Sheist!:
Anti-rollback (arb) information obtained below contains some unknowns. Please offer information with supporting links if you are aware of errors provided here.

Anti-rollback: what is it, why was it created, and how does it affect Xiaomi phones?

KNOWN:

- Xiaomi anti-rollback (arb) means prohibiting reinstalling a lower version stock software.

- Anti-RollBack is a mechanism that prohibits rollback to earlier versions of software. This applies to both firmware and pure Android phones. Breaking this system, the user will be faced with an instant “bricking” of the device.

- Google arb is compulsory for all Android 9 versions and up

- Unlocking the bootloader disables Google arb, but not Xiaomi arb. Unlocking the bootloader does not disable Xiaomi arb.

- Xiaomi arb has become obligatory on all Xiaomi smartphones starting Android 9

- Xiaomi arb was implemented initially to prevent fraudsters from buying cheaper Chinese and Indian phones and reflashing software to pass them off as multimedia devices.

It is extremely important to understand exactly how Xiaomi’s Anti Rollback works. In this regard, you should keep in mind that Verified Boot has a rollback index which is compared with the rollback index of the ROM that you are about to flash.

- If the current rollback index on your device is less than the rollback index in the ROM to be flashed, then the ROM will be flashed without any issues and the current rollback index will be increased to match the new rollback index [of the just flashed ROM].

- If the current rollback index on your device is equal to the rollback index in the ROM to be flashed, then the ROM will be flashed and there will be no change in the rollback index.

- If the current rollback index is greater than the rollback index in the ROM to be flashed, then the ROM will be rejected. But this will only happen if you’re flashing via fastboot or Mi Flash.

- However, if you are flashing the ROM via TWRP, then it will straightaway start the flashing process [as most TWRP builds don’t come with ARB check] and ultimately brick your device.

HOW TO VERIFY ARB SETTING ON PHONE:

- fastboot getvar anti

HOW TO VERIFY ARB SETTING ON MIUI ROM TO-BE-INSTALLED:

- Value of "X" in "set CURRENT_ANTI_VER=X" in flash_all.bat

WHAT DOES THE ARB ANTI NUMBER MEAN?

- If you don’t get any value [nil], then Anti Rollback is not implemented on your Xiaomi device. (NOTE: this statement conflicts with the earlier statement "Xiaomi arb has become obligatory on all Xiaomi smartphones starting Android 9")

- On the other hand, if you get a numerical value, then that is your device’s Anti Rollback Index.

- If “ARB:3” is displayed – you can safely roll back to the previous versions without any risk to the smartphone.

- If “ARB:4” is displayed – rollback will lead to “brick“.

UNKNOWN/UNCLEAR:

WHAT IS THE ARB VALUE OF THE CUSTOM ROM TO-BE-INSTALLED?

- unknown (NOTE: my testing indicates a custom ROM installation on a Xiaomi arb 3 custom ROM does not increase with subsequent custom ROM changes)

WILL XIAOMI ARB 1 INCREASE WITH SUBSEQUENT CUSTOM ROM INSTALLATIONS?

- unknown (NOTE: my testing indicates a custom ROM installation on a Xiaomi arb 1 custom ROM does not increase with subsequent custom ROM changes. Please post your findings if different.)

WHAT DO ARB VALUES 0 (or blank), 1 AND 2 MEAN?

- 0 (blank) means "Xiaomi arb is not implemented", but this conflicts with the earlier statement of "Xiaomi arb has become obligatory on all Xiaomi smartphones starting Android 9"

- 1 - unknown

- 2 - unknown

RECOMMENDATIONS:

- Do not install the wrong firmware.

- Do not install a prior stock ROM if you are not on a custom ROM first, particularly with a custom recovery like TWRP, as you risk an arb trip.

- Do not install a prior stock ROM if you are on a stock ROM; you risk an arb trip. The stock install scripts provided by MIUI should warn and prevent any arb trip prior to it occurring.

- Do not bypass MIUI install scripts (i.e. using TWRP) for stock-to-stock software installations, if you can help it. Otherwise, you risk an arb trip.

HOW TO BYPASS XIAOMI ARB AND PERFORM A DOWNGRADE:

- Google search, or link at the bottom

HOW TO RESOLVE A PHONE LOCKED BY XIAOMI ARB:

- only authorized EDL accounts (not all of them) can resolve this

LINKS THAT HELP EXPLAIN XIAOMI ARB MORE:

What Is Anti-rollback (ARB) On Xiaomi Phone With MIUI Firmware

Find the answer to your question ➔ Anti-RollBack (ARB) on Xiaomi ✓! Get the quick and easy solution right now.

xiaomilive.com

How to Check Xiaomi Anti Rollback Index and Prevent Brick

In this guide, we will show you the steps to check the Anti Rollback [ARB] Index on your Xiaomi device and prevent it from getting bricked.

droidwin.com

How to Bypass Xiaomi Anti Rollback and Perform a Downgrade

In this comprehensive guide, we will show you the steps to bypass Xiaomi Anti Rollback and perform a downgrade.

droidwin.com