I began identifying three existing virtualized solution, they are VMware, Microsoft HyperV and Oracle Virtual box . I am trying to identify which one is compatible with GNS 3 . However I am also looking for some shortfall in those solution for example, Hyper V does not allow an external switch to be used. Hyper V has 3 types of switches internal,private,external, but none of theses switch allows custom programming . I have added 2 other virtual servers to my existing solution, however after I promote the Domain Controller I run in some problem where I cannot add the two other servers to the domain .I am still learning about server because I am not verse in server 2012.More over , I also have some problem with the DNS services and DHCP services on the Domain Controller.