352-001 · Question #770
352-001 Question #770: Real Exam Question with Answer & Explanation
The correct answer is A: at the aggregation layer because it is the Layer 2 to Layer 3 demarcation point. In a three-layer data center design with a Layer 3-only core, the aggregation layer serves as the Layer 2/Layer 3 boundary and is the optimal termination point for a Layer 2 interconnection.
Question
Options
- Aat the aggregation layer because it is the Layer 2 to Layer 3 demarcation point
- Bat the core layer because all external connections must terminate there for security reasons
- Cat the core layer, to offer the possibility to isolate STP domains
- Dat the access layer because the STP root bridge does not need to with the HSRP
Explanation
In a three-layer data center design with a Layer 3-only core, the aggregation layer serves as the Layer 2/Layer 3 boundary and is the optimal termination point for a Layer 2 interconnection.
Common mistakes.
- B. The core is Layer 3-only in this design and does not participate in Layer 2 switching, so it cannot serve as a Layer 2 termination point regardless of any security policy.
- C. Terminating at the L3-only core is architecturally incorrect; STP domain isolation is achieved by keeping L2 at the aggregation layer, not by extending it upward to the core.
- D. STP root bridge placement is a separate design concern and does not dictate where a Layer 2 interconnect should terminate; the aggregation layer remains the correct L2/L3 demarcation point.
Concept tested. Layer 2 WAN termination in three-tier data center design
Reference. https://www.cisco.com/c/en/us/td/docs/solutions/Enterprise/Data_Center/DC_3_0/DC-3_0-CCDesign.html
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