Internal interfaces are generally for East-West traffic, while uplink interfaces are for North-South traffic.
An NSX Edge Services Gateway (ESG) can have up to 10 internal, uplink, or trunk interfaces. These limits are enforced by the NSX Manager. When a logical router (DLR) is connected to an edge services gateway (ESG), the interface on the router is an uplink interface, while the interface on the ESG is an internal interface. An NSX trunk interface is for internal networks, not external networks. The trunk interface allows multiple internal networks (either VLAN or VXLAN) to be trunked.
An NSX Data Center deployment can have up to a 1,000 distributed logical router (DLR) instances on a single ESXi host. On a single logical router, you can configure up to eight uplink interfaces, and up to 991 internal interfaces. These limits are enforced by the NSX Manager. For more information about interface scaling in an NSX Data Center deployment, see the NSX Network Virtualization Design Guide at https://communities.vmware.com/docs/DOC-27683.