NSX-T Data Center supports a 2-tier routing model.

In the top tier is the tier-0 logical router. Northbound, the tier-0 logical router connects to one or more physical routers or layer 3 switches and serves as a gateway to the physical infrastructure. Southbound, the tier-0 logical router connects to one or more tier-1 logical routers or directly to one or more logical switches.

In the bottom tier is the tier-1 logical router. Northbound, the tier-1 logical router connects to a tier-0 logical router. Southbound, it connects to one or more logical switches.
Note:

If you use Manager mode to modify objects created in the Policy mode, some settings might not be configurable. These read-only settings have this icon next to them: . See NSX Manager for more information.