Dynamic MAC Address Table: Volatility, Learning and Aging
Short answer
BCD Dynamic MAC entries are lost on reset or card hot-swap, are learned from received source MAC addresses with aging, and their count per interface shows active users.
Question
Key Takeaways
It tests the dynamic-versus-static MAC entry boundary; the trap is option A, whose loss-resistant behaviour belongs only to manually configured static entries, not to volatile learned ones.
This H12-811 question tests the dynamic MAC address table: entries are volatile and lost on reset or card hot-swap, are learned from source MAC addresses and age out, and their per-interface count reflects communicating users — so B, C and D are correct.
Common mistake: Option A is the tempting wrong choice: it describes static MAC entries, which are saved to configuration, whereas dynamic entries live in RAM and are erased on device reset, interface-card hot swap or card reset.
Expert Analysis
The boundary that matters: dynamic vs. static entries
The whole question turns on one distinction — where the entry came from and where it lives. A dynamic MAC entry is written by the switch itself into volatile memory: it learns the source MAC of frames arriving on an interface and installs it with a lifetime. A static MAC entry is manually configured, bound to a port (optionally a VLAN), written to non-volatile configuration storage, and therefore survives reloads. Option A describes exactly the static entry, so A is false and B is true: reset the device, hot-swap the card, or reset the card, and the dynamic entries in RAM are gone — they are rebuilt only as traffic flows again.
What the aging timer implies
Because the switch learns the source MAC address of each received frame and then ages the entry out when no traffic refreshes it before the aging time (Huawei default 300 s), D is true on both halves: learned-from-source and ageable. This is the mechanism that keeps the table from filling with stale hosts.
Reading user count from the table
C is also true. Each dynamic entry on an interface represents a source MAC seen on that port, so filtering the MAC table by a specific interface and counting its dynamic entries gives a direct count of the stations currently communicating there — this is a documented Huawei method for estimating active users per port. A community explanation states that "MAC table entries can reflect user count" and that documentation for some Huawei devices explicitly permits obtaining the number of users communicating on an interface this way.
So the correct set is B, C, and D, with A rejected as the static-entry behaviour.
Exam Strategy
On MAC table questions, first sort each statement by origin: entries the switch learns are dynamic and volatile, entries you configure are static and persistent. Read each option and ask "is this describing learning plus aging, or configuration plus storage?" — that single test separates A from B, C and D here. Also treat observability claims (counting entries to size traffic or users) as true unless they imply data the switch cannot see; source MACs per port are always visible.
Frequently Asked Questions
Why is option A wrong for dynamic MAC entries?
How can the MAC table show how many users are on an interface?
How does a switch learn and age dynamic MAC entries?
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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Fmoura17 👍 1The correct answers are B, C, and D. A. Dynamic MAC entries are not lost after reset or hot swap ❌ This is false. This description applies to static MAC address entries, which are manually configured and saved permanently. Dynamic MAC address entries are stored in volatile memory (RAM) and are lost whenever a device is reset, an interface card is hot swapped, or an interface card is reset.
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Heidorn 👍 1The answer is BCD, you ARE able to obtain the number of users communicating via said interface, by checking the dynamic MAC table it even says so on the documentation of some huawei devices regarding dynamic Mac address entries.
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e9b92a4 👍 1✅ Correct answers: B, C, and D OptionStatementCorrect?ADynamic MAC entries are not lost after reset❌BDynamic MAC entries are lost after reset✅CMAC table entries can reflect user count✅DDynamic MACs are learned and aged out✅
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