Which ACI Bridge Domain Setting Forces Remote Leaves to Delete EP1?
Short answer
B Set L2 Unknown Unicast to Flood (with Clear Remote MAC Entries) so every remote leaf deletes EP1 immediately instead of aging it out.
Question
Key Takeaways
The question tests how ACI propagates an endpoint deletion to all remote leaves when EP1 is replaced by EP2; the trap is assuming Hardware Proxy also purges remote MAC entries, when that behaviour is tied to the Flood setting.
In Cisco ACI, setting L2 Unknown Unicast to Flood on the bridge domain (together with Clear Remote MAC Entries) makes the local leaf tell every remote leaf to delete endpoint EP1 immediately instead of waiting for the endpoint aging timer. This page explains why option B, not Hardware Proxy, is the correct answer for replacing EP1 with EP2 on the same leaf.
Common mistake: The most common wrong pick is Hardware Proxy (options A and C), because it is the recommended production setting for L2 Unknown Unicast. Hardware Proxy does not expose Clear Remote MAC Entries, so remote leaves keep EP1 learned until the aging timer expires.
Expert Analysis
Why the Answer Is Correct
In Cisco ACI, the bridge domain parameter L2 Unknown Unicast is set to either Hardware Proxy or Flood. Only when it is set to Flood does APIC expose the Clear Remote MAC Entries option, which is exactly the mechanism the question describes. With that combination, when leaf1 detects that EP1 is gone and EP2 is learned locally, it signals every remote leaf where the bridge domain is deployed to delete the EP1 MAC entry right away. Without it, remote leaves continue to forward to EP1 until the endpoint aging timer expires, which is precisely the delay the question wants to avoid. Option B therefore names the setting that enables the immediate remote purge.
Why the Other Options Are Wrong
Options A and C are the same configuration ("Hardware proxy" versus "Hardware Proxy" — only capitalization differs): setting L2 Unknown Unicast to Hardware Proxy. Under hardware proxy, the fabric does not flood unknown unicast, and the Clear Remote MAC Entries option is not available, so a deleted local endpoint is not advertised for immediate removal by remote leaves. Unknown unicast is instead handled by the spine proxy, which does nothing to force remote leaves to drop EP1 early. That leaves the remote leaf MAC table stale until the timer expires, which is the opposite of the requirement. Option D ("Set L2 Unknown Unicast to Flood") is a duplicate of option B and equally correct in substance, but B is the letter selected here.
Community Comment Notes
One commenter, mms101, explains the mechanism very precisely, noting that with Flood "the system deletes it from both the local leaf switches as well as the remote leaf switches" and pairing it with the Clear Remote MAC Entries action, while warning that otherwise a remote leaf keeps the endpoint until the timer expires. prospio971 argues for Hardware Proxy plus a manual remote MAC clear, but manual clearing is an operational workaround rather than the fabric behaviour the question asks for, and that reviewer's own reasoning still depends on an explicit clear action. ed27 simply states "B is correct", which aligns with the documentation-based explanation. The vote split between A and B reflects how many candidates over-value hardware proxy as a general best practice; the clearing behaviour is what decides this question.
Exam Strategy
Read the qualifier "before timer expiration" as the deciding clue: it points to an active remote-MAC clearing feature rather than normal endpoint aging. Eliminate the Hardware Proxy options first (A and C are the same setting with different capitalization), then choose Flood (B, mirrored by duplicate D) as the setting that enables Clear Remote MAC Entries.
Frequently Asked Questions
Does setting L2 Unknown Unicast to Flood alone purge EP1 from remote leaves?
Why can't Hardware Proxy delete EP1 on remote leaves before the timer?
Community Votes
50% of anonymous learners picked answer B. 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
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mms101 👍 3B. When the bridge domain has L2 Unknown Unicast set to Flood, if an endpoint is deleted the system deletes it from both the local leaf switches as well as the remote leaf switches where the bridge domain is deployed, by selecting Clear Remote MAC Entries. Without this feature, the remote leaf continues to have this endpoint learned until the timer expires. https://www.cisco.com/c/en/us/td/docs/switches/datacenter/aci/apic/sw/2-x/L2_config/b_Cisco_APIC_Layer_2_Configuration_Guide/b_Cisco_APIC_Layer_2_Configuration_Guide_chapter_010.html#:~:text=When%20the%20bridge,the%20timer%20expires.
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prospio971 👍 1 Answered ABy setting L2 Unknown Unicast to Hardware Proxy and clearing remote MAC entries, the fabric ensures that all references to EP1 are removed promptly, allowing EP2 to be properly learned and avoiding traffic misdirection. It is not B: Setting L2 Unknown Unicast to "Flood" would result in unnecessary flooding of unknown unicast traffic across the fabric, which is inefficient and not recommended in ACI environments.
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ed27 👍 1 Answered BB is correct
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