Hello Mohammad
The truth is, there’s a lot there to get your head around! I’ll try to clear it up for you.
First of all we have the Network Virtualization Endpoint (NVE). This is the entity on which the VNI (VXLAN Network Identifier) is configured, and from where the multicast group functions. The NVE is “sourced” on a loopback interface. In other words, it adds the capability of VNI membership and multicast participation to the loopback interface it is sourced from.
Next we have the Ethernet Flow Point (EFP) service instance. This is a logical interface that is used to bind the bridge domain to a physical port. Put another way, the physical interface that faces towards the VXLANs being segmented is configured with a service instance so that traffic on this port is dealt with correctly. Service instances allow a single Ethernet port to process frames for multiple services. In this case, the configured service is the VXLAN functionality. More info on EFPs can be found here:
Finally, we have a bridge domain interface (BDI). This is essentially a virtual routed interface that represents a set of bridged (layer 2) interfaces. It basically allows a router to have two (or more) interfaces on the same subnet. IN such a case, a BDI would act as the routed interface for those two bridge physical interfaces, kind of like an SVI on a L3 switch. You can find out more info about this at the following Cisco documentation:
In the context of VXLANs, the BDI is the layer 3 interface that represents the physical interface and the loopback interface thus combining the configured VNI, the service instance, and the physical interface.
I hope this has been helpful!
Laz