300-540 Exam Dumps : Designing and Implementing Cisco Service Provider Cloud Network Infrastructure (SPCNI v1.0)

In a cloud-scale or data center–scale environment,Virtual Extensible LAN (VXLAN)is used as anoverlay technologyto transportLayer 2 segments over a Layer 3 underlay network. VXLAN encapsulates Layer 2 Ethernet frames inside UDP/IP packets, allowing broadcast, unknown unicast, and multicast (BUM) traffic and tenant Layer 2 domains to be extended across a routed IP fabric.

Key points aligned with Cisco Service Provider Cloud Infrastructure design principles:

VXLAN creates aLayer 2 overlay on top of a Layer 3 underlay.

TheVXLAN Network Identifier (VNI)provides a much larger segmentation space than traditional VLANs, enabling multi-tenancy at cloud scale.

Because the underlay is pure Layer 3 (IP routed fabric), VXLAN allows you tointerconnect Layer 2 segments between leaf switches or data centers over an IP/MPLS backbonewithout relying on large Layer 2 domains in the physical network.

Why the options evaluate as follows:

Option A: extends Layer 2 segments across the underlying Layer 3 infrastructure✅This is the core benefit of VXLAN in cloud-scale designs. VXLAN encapsulates Layer 2 frames intoIP/UDP headers, allowing isolated Layer 2 segments (per VNI) to be stretched across a routed IP network. This enables:

Multi-tenant Layer 2 connectivity across a distributed cloud fabric

Mobility of virtual machines or containers while keeping same IP/MAC addressing

Use of an IP-based leaf–spine or service provider underlay for scalability and resiliency

Option B: extends Layer 3 segments across the underlying Layer 2 infrastructure❌This is the opposite of what VXLAN does. VXLAN is explicitlyL2-over-L3, not L3-over-L2. Extending pure Layer 3 segments over Layer 2 is not the VXLAN use case.

Option C: reduces spanning-tree complexity across the Layer 2 infrastructure⚠️(Partially related but not the primary or direct benefit)In modern designs, the underlay isLayer 3 routed, and VXLAN overlays provide logical Layer 2 segments. This designavoids dependence on spanning tree in the fabric, whichindirectlyreduces STP complexity. However, the fundamental, exam-relevant benefit isL2 extension over L3, so C is not the best or most accurate answer compared to A.

Option D: eliminates the need for a Layer 3 underlay in the service provider infrastructure❌VXLAN absolutelyrequiresan IP (Layer 3) underlay for transport. VXLAN tunnels are built over a routed infrastructure (leaf–spine, MPLS/IP core, etc.). It does not remove the need for Layer 3; it depends on it.

Comprehensive and Detailed Explanation

For distancesgreater than 20 miles, valid inter-facility transport options must support:

Metro-scale connectivity

High bandwidth

Low latency

Carrier-grade reliability

Acarrier access Ethernet ring (MEN / Metro Ethernet)is designed for:

Interconnecting data centers or meet-me rooms

Distances far exceeding 20 miles

High-availability layer-2 or layer-3 transport

Why the others are invalid:

CAT6e→ maximum ~100 meters

Multimode fiber→ typically <2 km (~1.25 miles)

Private wireless→ not used for high-capacity DC interconnects, unreliable for core transport

Thus, the only correct carrier-grade method isCarrier access Ethernet ring.

Comprehensive and Detailed Explanation

For virtualization functions and operational reliability, the architecture must leverageCisco NSO (Network Services Orchestrator)capabilities. NSO provides:

Transactional service modeling

Automatic rollbackwhen any step of a transactional deployment fails

Real-time network-state visibilityvia NSO CLI and live device synchronization

End-to-end service lifecycle automation

Among the options:

Why B is correct

"Virtualization service modeling" fits NSO’s core design principle: model the service, not individual devices.

NSO’s CLI providesstate visibility, operational introspection, transaction logs, and commit details.

NSO’s transactional engine providesautomatic rollbackupon any device or service failure.

This option capturesfull lifecycle automation,real-time state visibility, andreliability, exactly as required.

Why others are incorrect

A: CLI NED alone does not provide real-time state visibility or automated rollback; manual rollback contradicts requirements.

C: Only focuses on service modeling + CLI, but doesnotinclude rollback or lifecycle automation.

D: Templates alone do not ensure rollback or real-time operational state.