Hello all -
Just a word of warning, so you can avoid the unpleasantness that I and a few others have experienced when upgrading from v3.x to v4.x: you must reboot RouterOS after the license update, or it will completely lock you out of the router and cease all routing functions 72 hours later - just as if you had updated to v4.x without updating the license. This happened to me with a RB1000 in production, which fortunately was detected and rebooted right away by data center staff. I then confirmed it a second RB1000 which I had recently pulled out of a data center. The good news is that a simple reboot restores all function.
In both instances, when I updated the license via winbox, the router has dropped my winbox connection right after the license update as if by design, forcing me to start a new connection. If you are not sitting right in front of the router when this happens, it may lead you to believe that the router rebooted itself. But it has not! Don't be fooled by the dropped connection, in neither of my license update did the router automatically reboot itself.
If you are upgrading from v3.25 or later and you follow the upgrade steps in the order given on the download page at mikrotik.com, this will never happen to you, because the license update is done before the RoS version update, which requires a reboot to complete. But if you are upgrading from an earlier version than 3.24, or you are just a non-conformist like me, you'll do the license update as the last step - and that's where you will get into trouble. The current documentation is not perfectly clear that the license update, which must be done within 72 hours of the software version update, *must* include a post-license update reboot. So be advised!
Cheers,
Ed