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352-001 · Question #681
352-001 Question #681: Real Exam Question with Answer & Explanation
The correct answer is D: Company ABC should adopt a full-mesh POP connectivity.. When customers experience poor convergence due to a Tier 1 provider's core outages, adopting a full-mesh POP topology for Company ABC eliminates single points of failure in the transport layer.
Question
Refer to the exhibit. Company ABC is a Tier 3 service provider that offers Layer 2 and Layer 3 transport for small/medium enterprise customers in the US. Most of their network is built on Layer 2 MPLS circuits from a Tier 1 provider. Many Company ABC customers are using overlay VPN technologies and independent routing protocols, and they are affected with unacceptable convergence time after every major outage in the core of the Tier 1 provider. Which long-term redesign increases network availability?
Exhibit
Options
- ACustomers replace their own overlay VPN service with the Company ABC Layer 3 VPN service.
- BCustomers fine tune their routing protocol for faster convergence
- CCompany ABC replaces the Layer 2 MPLS circuit from the Tier 1 service provider with dark fiber/
- DCompany ABC should adopt a full-mesh POP connectivity.
Explanation
When customers experience poor convergence due to a Tier 1 provider's core outages, adopting a full-mesh POP topology for Company ABC eliminates single points of failure in the transport layer.
Common mistakes.
- A. Migrating customers to Company ABC's L3 VPN does not change the underlying Layer 2 transport topology, so convergence problems caused by Tier 1 outages would persist.
- B. Fine-tuning routing protocol timers is a short-term mitigation that reduces convergence time but does not eliminate the outage impact or add redundancy to the network design.
- C. Replacing MPLS circuits with dark fiber is expensive, geographically constrained, and does not inherently provide redundancy unless paired with a topology change like full-mesh connectivity.
Concept tested. WAN topology redesign for high availability
Reference. https://www.cisco.com/c/en/us/td/docs/solutions/Enterprise/WAN_and_MAN/Design/WAN_Design_Guide.html
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