Hi,
There the SR comes in play.
The SR takes care of those services.
You need edge nodes to run SR (they can be virtual)
4.1
Tier-0 Gateway consists of two components: distributed routing component (DR) and centralized services routing component (SR).
4.1.2 Services Router
East-West routing is completely distributed in the hypervisor, with each hypervisor in the transport zone running a DR in its kernel. However, some services of NSX-T are not distributed, including, due to its locality or stateful nature:
● Physical infrastructure connectivity
● NAT
● DHCP server
● Load Balancer
● VPN
● Gateway Firewall
● Bridging
● Service Interface
● Metadata Proxy for OpenStack
A services router (SR) – also referred to as a services component – is instantiated when a service is enabled that cannot be distributed on a gateway.
A centralized pool of capacity is required to run these services in a highly-available and scale-out fashion. The appliances where the centralized services or SR instances are hosted are called Edge nodes. An Edge node is the appliance that provides connectivity to the physical infrastructure.