Cisco ACI L2Out Loop-Free Topology Actions
Short answer
BC Enable MCP on the ports between the leafs and spine switches and disconnect the link between Leaf3 and Leaf4 to maintain a loop-free topology.
Question
Key Takeaways
The exam tests knowledge of ACI's default forwarding behavior and how to handle external L2 connections without creating loops within the fabric itself.
This question addresses loop prevention in a Cisco ACI fabric with an L2Out deployment. The correct actions involve enabling MCP and disconnecting unauthorized leaf-to-leaf links to maintain the default loop-free architecture.
Common mistake: Many candidates choose A (LACP) because it seems like a standard way to bundle links, but they fail to recognize that adding redundant links between leaves without proper spanning tree or MCP configuration can create loops if not managed correctly, or they miss the critical need for MCP.
Expert Analysis
Why the Answer Is Correct
To accomplish a loop-free topology when deploying an L2Out in Cisco ACI, two key actions are required based on the options provided. First, implementing MisCabling Protocol (MCP) on ports is essential as it detects and mitigates physical layer loops caused by misconnections. Second, since the ACI fabric follows a default loop-free behavior (typically a Clos network where leaves do not connect directly unless specified), any existing or potential direct link between Leaf3 and Leaf4 that could cause a loop must be disconnected or prevented. While option C suggests disconnecting a specific link, the presence of such a link in the exhibit implies it's a potential loop source that needs removal.
Why the Other Options Are Wrong
Option A (Adding ports to LACP) is incorrect because simply bundling ports does not inherently prevent loops if the underlying topology allows for them; it just increases bandwidth. Option D (Implementing LLDP) is for discovery, not loop prevention. Option E (BPDU Guard) is relevant for edge ports connecting to end devices or external switches running STP, but MCP is the more comprehensive ACI-specific mechanism for internal fabric loop detection and mitigation in this context. The question asks for actions to accomplish a loop-free topology, implying active measures to ensure it, which includes removing invalid links (C) and enabling protection mechanisms (B).
Community Comment Notes
Comments show a split between C and A, with some users suggesting both A and C. One user noted 'A to avoid loops with external L2 network, C as ACI does not accept connectivity between LEAFs,' highlighting the structural constraint. Another user argued for B and E, focusing on BPDU guard and MCP, which aligns with best practices but might miss the specific topology fix implied by the exhibit showing a leaf-to-leaf link. The consensus leans towards correcting the physical topology (C) and enabling protocol-based protection (B).
Official Reference
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Exam Strategy
Always check the fabric design guidelines: default ACI fabrics do not support direct leaf-to-leaf links unless explicitly configured for specific use cases, making such links potential loop sources. Use MCP as your primary defense against physical misconfigurations that could break the loop-free assumption.
Frequently Asked Questions
Why is disconnecting Leaf3-Leaf4 necessary?
Is LACP sufficient for loop prevention?
Community Votes
40% of anonymous learners picked answer C. Votes are pick records left by other test-takers — they are not the verified answer.
Discussion 5 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 5
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mdriraa 👍 2 Answered CA to avoid loops with external L2 network, C as ACI does not accept connectivity between LEAFs.
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zelya19 👍 2Should be A, C as the question asks to choose two answers.
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prospio971 👍 1 Answered BShould be B & E: To ensure a loop-free topology when deploying an L2Out in a Cisco ACI fabric: Enable BPDU Guard to prevent external switches' STP behavior from influencing the fabric. Enable MisCabling Protocol (MCP) to detect and mitigate loops caused by cabling or misconfigurations.
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udo2020 👍 1 Answered AFrom my perspective there is only one answer right. This is A. It is not neccesary for mcp between leaf and spines because this is L3.
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mdriraa 👍 1 Answered AA,C to avoid loops
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