Mikrotik RB750UP 4/32 question

Had a few questions about this rb750up running openwrt. If choosing a non latest version (even v15, v16, or v18) would this router be able to run properly with sqm and dscp iptables? From what is known, the device is not able to be run (or barely) on v19 and past so would it be possible to run sqm, cake even, and dscp tables on older firmware (know about the security concerns but this is just a project). If it can run, which is the oldest firmware which has sqm and iptables.

Just so that you are aware...

  • Old versions, especially VERY old versions, are EOL and unsupported.
  • They will contain many known serious security vulnerabilities (that will never be patched) and should not be used anymore, especially if connected to the internet.
  • The syntax of the old versions is significantly different than the modern versions, so it is very likely that people will not remember how to help you with the configurations.
    • As stated above, the old versions are unsupported. Do not expect any help on the forums -- running such old versions should be considered both "on your own" and "at your own risk"

SQM and cake probably won't run on a device with only 32MB of RAM and 4MB flash when running 19.07. Maybe DSCP tables would work, but I wouldn't count on it.

Also, a 4/32 device also will have a very weak processor and therefore will be severely constrained in terms of bandwidth. Running traffic shaping will make that even more constrained.

Why even bother with hardware that is so old that you'd have to run ancient firmware? Anything you learn would have to be re-learned due to the fact that the syntax and capabilities are materially different.

You can buy many much more capable devices for relatively cheap -- especially on the used market.

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Are you sure it's a 4/32 device as mikrotik list it as 64/32 and I have two of them

According to the data on the device info page, yes it is a 32MB device.
https://openwrt.org/toh/mikrotik/rb750up

I stand corrected that it actually has 64MB flash storage (which is certainly interesting given how little RAM).

But... the RAM will be a severely limiting factor here... especially for the OP's desired use cases. And that is where the story really ends -- 32MB RAM is just not sufficient and it cannot run anything later than 19.07 (even that would be really poor performance with high likelihood of OOM errors).