In an EVPN-VXLAN architecture, the network is divided into two distinct planes: the Underlay and the Overlay.

Underlay (IP Fabric): The underlay ' s only job is to provide IP reachability between the loopback addresses of all VTEPs (Virtual Tunnel Endpoints). This is typically achieved using OSPF, IS-IS, or EBGP.

Overlay (EVPN Control Plane): The overlay is responsible for carrying Layer 2 MAC and Layer 3 IP reachability information between switches. EVPN signaling is the standard mechanism for this task.

Protocol Choice (Option D): EVPN uses MP-BGP (Multiprotocol BGP) as its control plane protocol. On Juniper EX Series and QFX Series switches, the most scalable and recommended design for the overlay is EBGP (External BGP).

In a 3-stage or 5-stage Clos architecture, EBGP is used in the overlay to exchange EVPN routes (Route Types 1-5) between Leaf and Spine switches.

EBGP simplifies configuration by avoiding the need for Route Reflectors (required for IBGP) and provides better control over route propagation through BGP community and policy management.

Incorrect Options:

Options A and B refer to the underlay protocols. While they provide the path for the VXLAN tunnels, they do not handle the EVPN signaling itself.

Option C (MPLS) is a different transport technology. While EVPN can run over MPLS (EVPN-MPLS), campus designs on EX series devices specifically use VXLAN as the data plane, making EBGP the standard signaling protocol for the EVPN-VXLAN overlay.