What is a benefit of using VXLANs in a cloud-scale environment?

Virtual Extensible LAN (VXLAN) is a network virtualization technology that creates a Layer 2 overlay network on top of a Layer 3 underlay infrastructure. It encapsulates Layer 2 Ethernet frames within Layer 4 UDP packets, enabling the extension of Layer 2 segments, or broadcast domains, across different physical locations over an IP network. This mechanism is crucial in cloud-scale environments for providing workload mobility and multi-tenancy, as it decouples the logical network from the physical network topology, overcoming the scaling limitations of traditional VLANs.

B. This is incorrect. VXLAN extends Layer 2 segments over a Layer 3 underlay, not the other way around.

C. While using a Layer 3 underlay with VXLAN eliminates the need for Spanning Tree Protocol (STP) in the fabric core, this is a consequence of the primary benefit, which is extending Layer 2 over Layer 3.

D. This is incorrect. VXLAN fundamentally requires a Layer 3 underlay network to provide IP connectivity between VXLAN Tunnel Endpoints (VTEPs) for packet transport.

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1. IETF RFC 7348: Mahalingam, M., et al. "Virtual eXtensible Local Area Network (VXLAN): A Framework for Overlaying Virtualized Layer 2 Networks over Layer 3 Networks." August 2014.

Section 1 (Introduction): "This document specifies Virtual eXtensible Local Area Network (VXLAN), which is a mechanism to overlay virtualized layer 2 networks over layer 3 networks... VXLAN is a Layer 2 overlay scheme over a Layer 3 network." This directly supports the correct answer (A) and refutes options B and D.

2. Cisco Systems, Inc. "VXLAN Overview: Cisco Nexus 9000 Series Switches, NX-OS Release 7.x"

"VXLAN Overview" section: "VXLAN (Virtual Extensible LAN) is a MAC-in-UDP encapsulation that allows you to create a Layer 2 overlay network on top of a Layer 3 underlay network." This statement confirms that VXLAN's purpose is to extend L2 over L3.

3. Cisco Systems, Inc. "VXLAN Network with MP-BGP EVPN Control Plane Design Guide"

"Introduction to VXLAN" section: "Virtual Extensible LAN (VXLAN) is a tunneling protocol that is designed to solve the problem of scaling in cloud computing environments. It runs an L2 overlay network on top of an L3 underlay network." This reinforces the core function described in option A. It also implicitly refutes option C as the primary benefit, framing the technology as a solution to scaling, which is achieved by the L2-over-L3 extension.