GTM upgrades

I have got two DC’s having 1-1 GTM’s and 2-2 LTM’s running 10.4 version. I have to upgrade them to 12.x version. First I am planning to upgrade the GTM’s one at a time.

So I upgrade DC1 GTM run the big 3d version command which would update the big 3d on the LTM’s as well so the LTM’s can establish the iquery fine.

My query is once I run the big3d command would it also update the big3d version on the DC2 GTM ? If yes then I am covered if not then I would fall into a scenario where my LTM’s are running higher version of big3d and DC2 GTM is running lower version of big3d would iquery still run fine between the LTM’s and DC2 GTM which is still on 10.4, otherwise the dns resolutions would start failing.

Can someone help what is the best way to upgrade to in such a set-up ?