300-420 · Question #21
300-420 Question #21: Real Exam Question with Answer & Explanation
The correct answer is D: VPLS. {"question_number": 2, "correct_answer": "D", "explanation": "VPLS (Virtual Private LAN Service) is the correct answer because it satisfies all three requirements. It operates at Layer 2 and provides a full-mesh logical topology across all sites in the VPN, fulfilling the Layer 2
Question
An enterprise customer has these requirements: - end-to-end QoS for the business-critical applications and VoIP services based on CoS marking. - flexibility to offer services such as IPv6 and multicast without any reliance on the service provider. - support for full-mesh connectivity at Layer 2. Which WAN connectivity option meets these requirements?
Options
- AVPWS
- BMPLS VPN
- CDMVPN
- DVPLS
Explanation
{"question_number": 2, "correct_answer": "D", "explanation": "VPLS (Virtual Private LAN Service) is the correct answer because it satisfies all three requirements. It operates at Layer 2 and provides a full-mesh logical topology across all sites in the VPN, fulfilling the Layer 2 full-mesh requirement. Because VPLS delivers a transparent Ethernet service, the customer retains complete control over Layer 3 protocols including IPv6 and multicast without any dependency on the service provider's routing capabilities. CoS (Class of Service) markings in Ethernet frames are preserved end-to-end, enabling customer-driven QoS policies. VPWS (A) is point-to-point Layer 2, not full-mesh. MPLS VPN (B) is a Layer 3 service where the SP controls routing, and multicast/IPv6 support depends on SP configuration. DMVPN (C) is an overlay tunnel solution that operates at Layer 3 and does not provide native Layer 2 full-mesh connectivity.", "generated_by": "claude-sonnet", "llm_judge_score": 4}
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