Today I had enough free time as I thought to update the RouterOS on my 2 Mikrotik routers from ver.6.45.1 to ver.6.45.2. So I did it as usal. Just copied new OS files from the appropriate section on Mikrotik official website (https://mikrotik.com/download
) devoted to RB4011 to the router file destination (Files\File list) and rebooted. What a great surprise I had finding out after reboot and upgrade that I had lost access to Internet. After carefull review I found out that my router lost it's ability to obtain the ip-address from ISP via DHCP. As my ISP provides dynamic ip-addresses only by DHCP that was really a quest. What made the situation worse was that I had not only upgraded the RouterOS but the firmware too. Now I know it's a bad habbit to upgrade both of them. Will never do such reckless things again. The good point was I always make backups in .backup and .rsc. So all configurations were safe. Buttt!!! It was a real brainstorm how to downgrade the firmware. As to the RouterOS - there was no problem and the process is clearly described in many sources. But I did a long investigation on third-party forums how to downgrade the firmware. Now I want to address to the Mikrotik support team. Why is there no information on Mikrotik official website? Please do your job. If anyone encounters such a problem - the issue is as follows:
1. Downgrade the RouterOS to the needed version (you can find the version you need here: https://mikrotik.com/download/archive
2. In New terminal window type: system routerboard upgrade (Yes,yes. This is not a mistake. You have to type not DOWNGRADE but UPGRADE!!! Though in fact your firmware will be downgraded to the current RouterOS version that you have downgraded to in the 1 step.
3. After a promt DO YOU REALLY WANT TO UPGRADE THE FIRMWARE Y/N just type Y and the firmware will downgrade!
4. Reboot the router.
But my bad luck at this time was not gone. After downgrading both firmware and RouterOS to the previous version my router still refused to obtain the ip-address from the ISP via DHCP. I got in touch with the ISP support and they checked that the switch port my RB is connected to is set properly (negotiation off, speed-duplex force1g-full nonegotiate slave) as only such settings work in RB4011 SFP+ cage when using SFP 1G modules. After the ISP confirmed that the settings meet my requirements I unplugged the RB4011 (pay attention, not rebooted but unplugged. As it turned out that on reboot the SFP module stays powered on) and in a minute plugged in again. The RB4011 booted and at this time obtained the ip-address via DHCP correctly without any issues.
I don't know what the Mikrotik engineers did wrong but I do strongly advise you not to update to RoterOS version 6.45.2 and keep away from it. They call it stable but my experience shows it's faulty. Hope all Mikrotik users are the same level skilled as me otherwise there are not so many ISPs who can or will offer as skilled support. My e-mail is SL4529@GMAIL.COM
if you have similar issues or any questions left.