Enabling MCP to Prevent Layer 2 Loops in ACI
Short answer
D Enable MCP globally to ensure fabric-wide coordination for detecting and preventing Layer 2 loops.
Question
Key Takeaways
The exam tests the distinction between local and global scope for MCP policies; the trap is enabling it only locally, which fails to prevent fabric-wide loops.
This question addresses the configuration of MAC Control Protocol (MCP) within a Cisco ACI fabric to mitigate excessive Layer 2 loops. It establishes that MCP must be enabled globally to function effectively across the fabric infrastructure.
Common mistake: Candidates often select 'Enable MCP locally' (Option A/B), assuming that per-port configuration is sufficient, ignoring that MCP requires global coordination to detect and block loops across the entire fabric.
Expert Analysis
Why the Answer Is Correct
To effectively detect and prevent Layer 2 loops in a Cisco ACI fabric, the MAC Control Protocol (MCP) must be enabled globally. As noted by community member marceaubueno, "For MCP to work, it must be enabled globally and per-interface". The global policy ensures that the fabric controller coordinates the detection and response (such as err-disabling the interface) consistently across all nodes, rather than just on a single leaf port.
Why the Other Options Are Wrong
Options suggesting 'Enable MCP locally' are incorrect because local configuration only affects the specific interface or leaf where it is applied. Without the global instance, the fabric lacks the centralized logic to manage loop prevention holistically, leaving other parts of the fabric vulnerable to loops or unable to react uniformly to MCP packets.
Community Comment Notes
The community consensus strongly supports Option D. User zelya19 provided the navigation path: "Fabric > Access Policies > Policies > Global > MCP Instance Policy default", confirming the global scope requirement. Another user, designated, simply affirmed that D is correct, aligning with the official answer key.
Exam Strategy
Always check the scope of network protocols in ACI questions. If a feature like MCP, STP, or BGP needs to coordinate behavior across multiple devices or the entire fabric, look for the 'Global' option first before considering local/interface-specific settings.
Frequently Asked Questions
Does enabling MCP locally prevent loops?
Where is the MCP global policy configured?
Community Votes
100% of anonymous learners picked answer D. Votes are pick records left by other test-takers — they are not the verified answer.
Discussion 3 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 3
-
marceaubueno 👍 2D is correct. For MCP to work, it must be enabled globally and per-interface (attach the MCP policy under the interface policy group you have configured). If the ACI fabric receives an MCP packet on any interface, it will take action (could be just alerting with a fault, or err-disabling the interface on which the MCP packet was received).
-
zelya19 👍 2 Answered DFabric > Access Policies > Policies > Global > MCP Instance Policy default Fabric > Access Policies > Policies > Interface > MCP Interface
-
designated 👍 1 Answered DD is correct
Reader comments & corrections
No reader corrections yet — spotted an error or have a note? Share it below.