Core Switch Interconnect: Link Aggregation vs Spanning Tree
Short answer
C Configure link aggregation to bundle multiple physical links into a single logical channel, satisfying fault tolerance, increased bandwidth, vendor interoperability, cost effectiveness, and simplified management.
Question
• Fault tolerance and redundancy
• Vendor interoperability
• Increased bandwidth
• Cost effectiveness
• Simplified management
Which of the following should the administrator configure?
Key Takeaways
The question tests the ability to distinguish between loop prevention (STP) and capacity aggregation (LACP), identifying that only the latter satisfies the bandwidth requirement.
Learn why link aggregation is the correct configuration for core switch interconnections to meet redundancy, bandwidth, and management goals in N10-009 exams.
Common mistake: Candidates often choose Spanning Tree because it provides redundancy, but they overlook that STP blocks redundant links, failing the 'increased bandwidth' requirement.
Expert Analysis
Link Aggregation Meets All Constraints
The scenario demands a solution for core switch connections between data centers that balances redundancy, bandwidth, cost, and management. Link aggregation (such as IEEE 802.3ad/LACP) is the only option that satisfies all five requirements simultaneously. By bundling multiple physical links into a single logical channel, it provides increased bandwidth through load balancing across the member ports. It ensures fault tolerance and redundancy because if one link fails, traffic automatically shifts to the remaining active links without dropping the connection. The use of standardized protocols like LACP ensures vendor interoperability, allowing devices from different manufacturers to form bundles. Furthermore, it offers cost-effectiveness by utilizing existing cabling infrastructure rather than requiring expensive single high-speed interfaces, and it simplifies management by presenting the bundle as a single logical interface.
Why Spanning Tree is the Primary Trap
Spanning Tree Protocol (STP) is the most attractive but incorrect answer because it directly addresses two of the listed requirements: fault tolerance and redundancy. However, STP operates by blocking redundant paths to prevent loops, which means those blocked links provide zero bandwidth contribution. This fails the "Increased bandwidth" requirement entirely. Additionally, while STP prevents loops, it does not aggregate capacity or simplify management in the way link aggregation does; it actually adds complexity by dynamically altering port states based on topology changes. Comments correctly identify that while STP is essential for loop prevention, it cannot deliver the performance and management benefits required here.
Other Options Fail Specific Criteria
Increasing interface speeds to 10GB (Option B) increases bandwidth but does not inherently provide redundancy unless combined with other mechanisms, nor does it necessarily simplify management or guarantee vendor interoperability compared to standard aggregation protocols. Jumbo frames (Option D) increase payload size but do not address redundancy, bandwidth scaling via multiple links, or management simplification.
Exam Strategy
When evaluating network design options, cross-reference every requirement against each option. If an option satisfies some but fails a critical constraint like 'bandwidth' or 'interoperability', eliminate it. For redundancy questions, ask if the solution blocks traffic (STP) or utilizes it (LACP).
Frequently Asked Questions
Does link aggregation require specific hardware?
Can STP and Link Aggregation coexist?
Discussion 1 contributions
Compiled from public community threads and reader submissions, lightly edited for clarity. Handles and vote tallies are shown as recorded, and comments reflect the views of individual contributors.
From public community threads 1
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ERB14 👍 1 Answered CLink aggregation (such as LACP / IEEE 802.3ad) bundles multiple physical network links into a single logical channel to satisfy all listed requirements: Fault tolerance and redundancy: If one link in the aggregated bundle fails, traffic instantly shifts to the remaining active links without dropping the connection. Vendor interoperability: It uses standardized protocols (like IEEE 802.3ad LACP) supported across all major network hardware vendors. Increased bandwidth: Combining links multiplies throughput across the aggregated interface. Cost effectiveness & simplified management: It utilizes existing links to increase capacity and treats the bundle as a single logical interface for policy management.
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