Starting in NSX-T Data Center 3.0.2, you can migrate an NSX Data Center for vSphere environment that uses a collapsed cluster.
In a collapsed cluster design, all management VMs, workload VMs, and optionally edges run on the same vSphere cluster that is prepared for NSX for vSphere. The management VMs of the NSX-T Data Center must be initially attached to dvPortgroups. After migration, the management VMs of NSX-T Data Center will be attached to NSX-T VLAN segments.
The management VMs in the NSX-T Data Center include appliances, such as NSX Manager, vCenter Server, VMware Identity Manager, and so on. The NSX-T VLAN segment ports to which these management VMs connect are blocked after the migration when these management VMs are rebooted. Therefore, the management VMs might lose connectivity after the VMs reboot.
To prevent this problem, create a "management_vms" tag category, and add tags in this category. Assign a tag from this category to all the management VMs in the NSX-T Data Center environment. The migration coordinator migrates the VMs, which have tags in the "management_vms" tag category, always to use the unblocked VLAN segment ports.