The management plane is built by the NSX Manager, the centralized network management component of NSX Data Center for vSphere. It provides the single point of configuration and REST API entry-points.
The NSX Manager is installed as a virtual appliance on any ESXi host in your vCenter Server environment. NSX Manager and vCenter have a one-to-one relationship. For every instance of NSX Manager, there is one vCenter Server. This is true even in a cross-vCenter NSX environment.
In a cross-vCenter NSX environment, there is both a primary NSX Manager and one or more secondary NSX Manager appliances. The primary NSX Manager allows you to create and manage universal logical switches, universal logical (distributed) routers and universal firewall rules. Secondary NSX Managers are used to manage networking services that are local to that specific NSX Manager. There can be up to seven secondary NSX Managers associated with the primary NSX Manager in a cross-vCenter NSX environment.