Table of Contents
Question
Company XYZ, a global content provider, owns data centers on different continents. Their data center design involves a standard three-layer design with a Layer 3-only core. HSRP is used as the FHRP. They require VLAN extension across access switches in all data centers, and they plan to purchase a Layer 2 interconnection between two of their data centers in Europe.
In the absence of other business or technical constraints, which termination point is optimal for the Layer 2 interconnection?
A. at the core layer, to offer the possibility to isolate STP domains
B. at the aggregation layer because it is the Layer 2 to Layer 3 demarcation point
C. at the access layer because the STP root bridge does not need to align with the HSRP active node
D. at the core layer because all external connections must terminate there for security reasons
Answer
B. at the aggregation layer because it is the Layer 2 to Layer 3 demarcation point
Explanation
The correct answer to the question is B. At the aggregation layer because it is the Layer 2 to Layer 3 demarcation point.
When considering the optimal termination point for a Layer 2 interconnection between two data centers in the scenario provided, it is recommended to terminate the interconnection at the aggregation layer. Here’s a comprehensive explanation:
- Three-Layer Design: The company’s data center design follows a standard three-layer model consisting of the access layer, aggregation layer, and core layer. This design is commonly used to provide scalability, flexibility, and separation of functions in data center networks.
- Layer 2 to Layer 3 Demarcation: The aggregation layer serves as the demarcation point between Layer 2 and Layer 3 domains in the data center network. It is responsible for aggregating connections from the access layer switches and providing connectivity to the Layer 3 core.
- VLAN Extension: The company requires VLAN extension across access switches in all data centers. This means that VLANs need to be extended or stretched across multiple locations, allowing devices in different data centers to be part of the same Layer 2 broadcast domain.
- Layer 2 Interconnection: The company plans to purchase a Layer 2 interconnection between two of their data centers in Europe. Placing the termination point for this interconnection at the aggregation layer aligns with the Layer 2 to Layer 3 demarcation point. It ensures that the Layer 2 extension is contained within the data center environment and does not unnecessarily span across the core layer or external connections.
5. Optimized Design: By terminating the Layer 2 interconnection at the aggregation layer, the company can achieve optimized design and operational benefits. It allows for better control and isolation of spanning tree protocol (STP) domains, reduces the impact of Layer 2 loops or broadcast storms, and enables efficient routing and management of traffic at the Layer 3 core.
The other options listed in the question are not the optimal choices for the termination point of the Layer 2 interconnection:
- Terminating the interconnection at the core layer (A or D) would introduce Layer 2 extension into the core layer, which is typically designed for Layer 3 routing. This can increase complexity, potential risks, and complicate network operations.
- Terminating the interconnection at the access layer (C) is not recommended because the access layer is typically where end-user devices and hosts connect. Placing the Layer 2 interconnection at the access layer could lead to unnecessary broadcast traffic and suboptimal routing.
In summary, in the scenario provided, it is optimal to terminate the Layer 2 interconnection between two data centers at the aggregation layer. This choice aligns with the Layer 2 to Layer 3 demarcation point, provides better control and isolation of STP domains, and ensures efficient design and operation of the data center network.
Reference
- Data Center Interconnect Design Guide for Virtualized Workload Mobility with Cisco, EMC, and VMware – Cisco Virtualized Workload Mobility Design Considerations [Support] – Cisco
- Configure a Layer 2 vPC Data Center Interconnect on a Nexus 7000 Series Switch – Cisco
- Layer 2 Data Center Interconnect – Reference Designs (site.com)
- Layer 2 Data Center Interconnect options | Network World
Cisco Certified Design Expert CCDE v3.0 400-007 certification exam practice question and answer (Q&A) dump with detail explanation and reference available free, helpful to pass the Cisco Certified Design Expert CCDE v3.0 400-007 exam and earn Cisco Certified Design Expert CCDE v3.0 400-007 certification.