Hello. I am in the process of migrating from SBS 2008 to Windows Server 2012 R2. I have transferred all 5 FSMO roles to the the new server and removed the SBS 2008 server as a Global Catalog server. In addition, DHCP has been moved to the Windows 2012 R2 server. Everything seems to be running okay. Before I DCPROMO the SBS 2008 server and remove it from the network, I wanted to test things so I disconnected the network cable from the SBS 2008 server. This seems to have had an impact on internet communications as browsing to web pages seems to take a long time with messages of "Resolving host". Eventually everything loads, but it is nowhere near as fast as when I reconnect the SBS 2008 server. The DHCP server is pointing to the new server for DNS and the new server has itself listed as the DNS server. Ipconfig on clients point to the new server as well for DNS.
Is this issue because I have not DCPROMO'd the old server? Or could there be somewhere else that I need to check?