I am upgrading our domain controllers from 2008 to 2012r2.  I have a new dc that is 2012r2 (vm) and I have transfered the roles and GC.  The last step is DHCP.  I am in that process but ran into issue with our VLAN not getting IP addresses from new DHCP server.  It will only get from old DHCP server.  I have done a complete backup and restore and everything transfered but still no IP's given to vlan.  I am sure the issue is the router is setup to point to DHCP helper address to the old DHCP server.  I don't have access to that router to make that change.  I am hoping I can demote the old dhcp server and place that IP address into the new DHCP server (temporarily) so that IP addresses are issued properly during the time I wipe and install Win2012r2 on that domain controller (physical server).  Once the physical server is loaded with Windows 2012r2 and promoted I will place DHCP back and then restore that IP address.

Does this sound OK.  Do you foresee any problems that might be created with this?

Hi

 Correct the issue from ip helper,if it points to old dhcp server,clients still try to get ip from this old dhcp.You plan seems to be OK.

 And also you could configure dhcp on a member server.Then when you demote this old dhcp from domain.Last step will migrate dhcp from old to new one and change the ip adrress on new dhcp same to old dhcp.