A network topology system for reducing the hardware links in a centrally-controlled network having a plurality of network switches and a plurality of centralized controllers controlling those switches. The global network of switches and controllers is broken up into domains, wherein a domain contains a subset of controllers and switches, and a switch in a domain is controlled by one or more controllers. In-band hardware links, which carry both data and control information, are used to connect the controllers and switches in a domain, and thereby reduce the number of hardware links from that used in networks which have separate hardware links for both data and control information.