Tier-1 Gateway (also known as Tier-1 Logical Router): provides default gateway services for VMs attached to segments. It connects to one tier-0 gateway for northbound connectivity and one or more overlay networks for southbound connectivity.
Both types of gateways can include a distributed router (DR) and a service router (SR). Distributed routers are instantiated on transport nodes while service routers are being executed within NSX-T edge nodes. Service routers provide centralized functions such as NAT or load balancing.
How to deploy a T1 GW
Networking > connectivity > Tier-1 GW
Add Tier-1 GW
Provide a name for the T1 GW
For demonstration I am not selecting a T0 but will deploy later
Enable all static routes
Enable all connected segments and service ports
Confirm status is successful
In addition, you can add a segment to a T1 GW