Does it make any problems ? I could not find answer for it. I have not noticed problems but I want to be sure.

Hmm, difficult question. Looking at it from a general technical standpoint I would figure the following.

Newer versions often offer newer functionality or changes in protocol, drivers or how it needs to be addressed. So the same changes in RouterOS will be coupled with a certain firmware version.

If you are running an older RouterOS version with a newer version of the firmware you could run into a situation where the firmware expects command B (introduced in ROS 6.21) but you are running ROS 6.10 and thus it sends command A. That would result in a problem.

Ofcourse, you can be lucky and that it only has updated device drivers which accept the same commands. Then it won't be a problem.

I'm guessing only Mikrotik will be able to answer the question for your specific versions (Which you did not list!) but even then, it is not recommended or guaranteed to work at all.

Firmware is not changing as fast as ROS so it should be version matrix with accepted firmware/ROS combinations.

Normally you can upgrade RouterBOOT and leave RouterOS the same. Usually there are no such problems, I can't remember any situation like this.

Even if you run into a problem, you can always hold the reset button to start your device (this will load backup-routerboot version).

But I want to test 6.22 with latest firmware on my test 951G with stable 6.7. What if I upgrade it and then will want go back to 6.7.
It is not a problem of going back and forth with 3.xx, 4.yy, 5.zz and 6.nn.....but this particular process could be interesting for others.

Like I said, new RouterBOOT should not have any problems with old RouterOS. If you downgrade the device back to v6.7, it should work fine, even if the device runs new RouterBOOT firmware (3.19 or similar).

A word of warning though, never downgrade a RouterBOARD device below the version it was shipped with. New hardware revisions are sometimes not compatible with older RouterOS versions.

So if you received this unit with 6.18, do not downgrade to 6.7

Normis.....I bet that not too many users remember and saved ROS version of shipped devices.
Last week I have unpacked brand new 951G-2Hnd with 5.6 ROS so it works with 5.yy but some could receive it with 6.nn so two users could have misconception on minimal working version.

You can also downgrade the routerboot if you downgrade the ros and then upgrade the routerboot to lower version contained in actual ros. At least I think so - not able to test now.

Normis.....I bet that not too many users remember and saved ROS version of shipped devices.
Last week I have unpacked brand new 951G-2Hnd with 5.6 ROS so it works with 5.yy but some could receive it with 6.nn so two users could have misconception on minimal working version.

devices can be from different batches, so there will be actual physical changes, like nand or ram to name the few. This is why the wording - do not downgrade below version you received your new equipment.

You can also downgrade the routerboot if you downgrade the ros and then upgrade the routerboot to a lower version contained in actual ros. At least I think so - not able to test now.

You can upgrade and downgrade RouterBOOT (bootloader) similar as you can do with RouterOS. RouterOS by default includes bootloader in it. When you execute '/system routerboard upgrade' it will load that bootloader as primary one and use it. Or you can get fwf file and upload it to rood dir (in files menu) - that file will be written to primary bootloader.

But again - do not downgrade below version you received your router with.

you can see original version of bootloader by loading secondary bootloader that can only be installed in factory.

Also, just to help turn down the fear knob a bit, if you downgrade either RouterBOOT or RouterOS past the version that a certain board shipped with, and it doesn't work, you have not bricked the board. It is reversible and fixable without RMA; it's not like installing the wrong software will cause physical damage. For RouterOS, just Netinstall a newer version and keep the existing config when you do so. For RouterBOOT, use the backup bootloader to get it started again and then flash a new RouterBOOT to primary.

The danger is in downgrading a production device, or one that is remote. You will be able to fix it, but for a production router, you will incur some downtime, and for a remote router, you will have to physically go on-site to undo the damage.

-- Nathan

So I have future request: stored in ROM minimal ROS/firmware version which be consulted during downgrade process to block too old version to be installed.

It would be smart. Something like original mac addresses at Ethernet...

for routers with larger NAND you can create another partition and install RouterOS there
check '/partitions' menu

it will not help with wrong bootloader. but if you have working backup on another partition, you can set up failover.

Yes, I use partitions. Unfortunately when booting main partition and the device looses power during the boot it starts from backup partition next time. But it is not the point we talk here. Why to waste so much disk space for some few byte long value?

OS updated are not mere bytes - that is whole OS fo the hardware. Use it to protect yourself for remote upgrades etc.

And it is a router anyway.

Janisk,

We are talking about downgrade, not upgrade.
There are already some threads: "I have downgraded to ROS yy.xx and my router is a brick now.".
If you do not want to change ROS with this maybe you could just print the minimal ROS version for the device on this device. Sticker will be easy to prepare and for cased devices there is already stick with MAC addresses so just add this info.

Few bytes and few lines of code could save you and us lot of time.