In the Nuage Networks Virtualized Network Services (VNS) architecture, the Network Services Gateway (NSG) is responsible for extending the overlay network to branch locations. For VLAN-based VPNs, the NSG encapsulates the Layer 2 traffic from the local network into VXLAN packets. These packets are then tunneled across the underlay WAN infrastructure to other NSGs or data center gateways. This VXLAN tunnel constitutes the data plane for the overlay network, enabling secure and isolated communication between sites. The control plane, managed by the Virtualized Services Controller (VSC), uses protocols like MP-BGP and OVSDB to distribute reachability information and program the NSG's forwarding state, but the actual user traffic is forwarded via VXLAN.

A. OpenFlow is a control plane protocol used by the VSC to program the NSG's forwarding tables, not for NSGs to exchange routing information directly with each other.

B. VXLAN is a data plane encapsulation protocol used to tunnel user traffic. It is not a control plane protocol for exchanging routing information.

C. OpenFlow is a control plane protocol for programming network devices; it is not a data plane tunneling protocol used for forwarding overlay traffic.

1. Nokia Nuage Networks, Virtualized Network Services (VNS) User Guide, Release 21.10.R1. In the "VNS Core components" section, the role of the NSG is described: "The NSG is a gateway that is located at a branch office or data center. It is managed by the VSC and establishes VXLAN tunnels with other NSGs or with a VRS-G for data traffic." This confirms VXLAN is the data plane tunneling protocol.

2. Nokia Nuage Networks, Virtualized Network Services (VNS) Fundamentals Student Guide, TTP33011-1-1. Module 2, "VNS Solution Architecture," describes the data plane operation. It explicitly states that the NSG encapsulates traffic from the LAN side into VXLAN packets for transport over the WAN, forming the overlay network.

3. Nokia, Nuage Networks from Nokia Virtualized Network Services (VNS) – SD-WAN Solution, Solution Description. In the section "The Nuage Networks VNS solution," it details the architecture: "The Nuage Networks VNS uses a VXLAN-based overlay model to provide L2 and L3 VPN services... The NSG establishes secure data plane connections using VXLAN-in-IPsec tunnels over the WAN." This confirms VXLAN is the foundational data plane technology.