Out of curiousity, do you need to export anything?
In the past I have
a) reduced lease length to very short
b) set up (but not activated) scope on new server
c) disabled scope on old server
d) waited for lease renewals (remember clients will try to retain the old IP
I appreciate that with a lot of reservations, you might not want to do that, though
Thanks – exporting is not essential, but it does create the scope. It also allows for an immediate migration as Server Manager requests the new server to be authorised, the old server is de-authorised and the present leases are in place. At least, this is how it worked migrating from 2008 to 2012 R2. I only have three reservations.