What Is a Function of MAC Learning on a Switch?

200-301 By islever Editorial Last updated

Describe switching concepts

Short answer

D A static MAC address entry is manually added to the switch's MAC address table, the only factually correct option given.

Question

What is a function of MAC learning on a switch?
  1. MAC address learning is disabled by default on all VLANs.
  2. Frames received for a destination MAC address not listed in the address table are dropped.
  3. The MAC address table is used to populate the ARP table.
  4. A static MAC address is manually added to the MAC table. Correct Answer

Key Takeaways

The question tests whether you know how a switch's MAC address table behaves, and the trap is that three of the four options state something false about switching or ARP, so you must pick the least-wrong, factually accurate statement rather than a perfect description of dynamic learning.

MAC learning lets a switch dynamically build its MAC address table (CAM table) by reading the source MAC address of every received frame and associating it with the ingress port. On this CCNA 200-301 question the only factually true option is D, because a static MAC entry is manually added to that same MAC address table — even though a manual entry is technically not 'learning' in the dynamic sense.

Common mistake: Many learners choose C, believing the MAC address table populates the ARP table. That is incorrect: MAC learning operates at Layer 2 and records MAC-to-port mappings, while ARP resolves IP addresses to MAC addresses at Layer 3 and is maintained separately by hosts and routers, not written by switch MAC learning.

Expert Analysis

Why the Answer Is Correct

Option D states that a static MAC address is manually added to the MAC address table, and that statement is factually true — an administrator can configure a permanent entry with a command such as mac address-table static <mac> vlan <id> interface <int>, and it will not age out like dynamic entries. Since this poorly worded question asks for "a function of MAC learning" and none of the options describe dynamic source-MAC learning accurately, the correct approach is to select the only option that is a true statement about the MAC address table. As NewJeans put it, "Even if D is not MAC learning, C is not correct statement" and "Only D is true among the selections." Static entries are still installed in and used by the MAC address table, so D is the defensible choice.

Why the Other Options Are Wrong

Option A is false because MAC address learning is enabled by default on switch ports; it is not disabled on all VLANs — without learning, a switch could never build a table and would behave like a hub. Option B describes a behavior that only applies to VLANs or ports with port security / unknown-unicast drop features enabled; by default, a frame for an unlisted destination MAC is FLOODED out all other ports in the VLAN, not dropped, which is how the switch discovers where the destination lives. Option C is wrong because MAC learning is a Layer 2 function that maps MAC addresses to ports, while the ARP table maps IP addresses to MAC addresses; as ricky1802 summarized, "MAC table - layer 2 ARP - layer 3." The switch does not use MAC learning to populate anyone's ARP table.

Community Comment Notes

The comments split between C and D, and the C-voters argue purely on terminology: HennieB wrote "The question specifically says LEARNING. A Static MAC is not learned," and mda2h cited a Cisco PDF stating a static MAC is not learned. That is terminologically fair, but it does not rescue C, because C's claim about populating the ARP table is factually wrong. The D-voters, including dropspablo and ricky1802, correctly dismiss A and B as well and note that D is the only true statement. Others questioned the question's quality altogether — Joshua25 complained the items are "full of logic errors, incorrect use of terms" — which is why the practical exam strategy is to eliminate the false statements and choose the remaining true one.

Official Reference

https://www.cisco.com/c/en/us/td/docs/optical/cpt/r_972/cpt95_configuration/cpt93_configuration_chapter_01100.pdf

This link opens the official vendor documentation in a new tab.

Exam Strategy

On CCNA questions with an awkward stem, treat the options as true/false statements and eliminate the ones that are factually wrong, even if none perfectly answers the wording. Remember the defaults: MAC learning is on, unknown unicast is flooded (not dropped), and the MAC table (MAC-to-port, Layer 2) is completely separate from the ARP table (IP-to-MAC, Layer 3).

Frequently Asked Questions

Why isn't C correct — doesn't the switch build the ARP table from MAC learning?

No. MAC learning records MAC-to-port mappings in the Layer 2 MAC (CAM) table; the ARP table maps IP addresses to MAC addresses and is built by ARP exchanges on hosts and routers, not by switch MAC learning.

What really happens to a frame whose destination MAC is not in the address table?

By default the switch floods the frame out all other active ports in the same VLAN (unknown unicast flooding) to locate the destination. It is only dropped if a feature such as port security or an unknown-unicast drop is configured.

If a static MAC entry isn't 'learning', why is D the answer?

Because every other option is factually false: learning is enabled by default, unknown unicast is flooded not dropped, and MAC learning never populates the ARP table. D is the only true statement about the MAC address table.

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Discussion 50 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 30 of 50

  1. HennieB 👍 32 Answered C
    The question specifically says LEARNING. A Static MAC is not learned
  2. dropspablo 👍 25 Answered D
    A. Wrong - MAC address learning is generally enabled by default on switches. B. Wrong - in this case the next step would be to replicate the original frame to the remaining ports (flood), in order to find the destination. C. Wrong - MAC learning on a switch (MAC table) is not used to populate the ARP table. MAC learning takes place at the layer 2 level of the OSI model, while the ARP table is related to layer 3, the IP protocol. The ARP table is populated by the host's response frame from the searched IP address destination (ARP reply). D. Correct - in MAC table learning, the addresses are learned by dynamically received frames, but it can also be learned statically, adding manually, when you want to force a destination for a specific host. Perhaps, in this case the static form can be considered a form of learning.
  3. Anonymous learner 👍 9
    Yeah, it is. It learns it from your manual input. This is different to "dynamic learning", i.e. using the source MAC address of an incoming frame, but it's still learning it. Put it another way; you're "teaching it" to associate the MAC address with a given interface number. Conversely, it is therefore "learning" from you. Good day sir.
  4. Joshua25 👍 5
    Actually, I am starting to doubt whether these are real CCNA questions. They are full of logic errors, incorrect use of terms, misinterpreted textbook sentences. Could some of them are fake questions purposely released to the internet by Cisco to confuse learners? As a leader in the networking industry, Cisco cannot even find someone who has normal English literacy and normal intellectual level to create some questions that make sense to human readers?
  5. mda2h 👍 5 Answered C
    Statically adding a MAC address is not concidered MAC learning, CISCO's words: https://www.cisco.com/c/en/us/td/docs/optical/cpt/r_972/cpt95_configuration/cpt93_configuration_chapter_01100.pdf
Show 25 more comments
  1. ricky1802 👍 5 Answered D
    Correct answer is D. MAC table - layer 2 ARP - layer 3
  2. 4aynick 👍 5
    arp is 2 layer protocol
  3. zamkljo 👍 4
    D is correct! I think MAC learning is about learning the unknown MAC Addresses, not matching the MAC addresses and IP addresses(ARP Table). Each switch has an ARP (Address Resolution Protocol) table to store the IP addresses and MAC addresses of the network devices. The ARP table is used to determine the destination MAC addresses of the network nodes, as well as the VLANs and ports from where the nodes are reached.
  4. Naghini 👍 4 Answered D
    C - incorrect, MAC table is for layer 2 switches , ARP table - layer 3 (routers and hosts use it). D - correct. A static entry in a MAC table is only possible if it's inserted manually.
  5. NewJeans 👍 4 Answered D
    Even if D is not MAC learning, C is not correct statement. MAC address table has nothing with the ARP table. Only D is true among the selections.
  6. BarkingSpider 👍 4 Answered C
    a static MAC is manually assigned, not learned.
  7. linuxlife 👍 3
    A switch can learn MAC address in two ways; statically or dynamically. In the static option, we have to add the MAC addresses in the CAM table manually. In the dynamic option, the switch learns and adds the MAC addresses in the CAM table automatically. The switch stores the CAM table in the RAM. The RAM is a temporary memory. All contents stored in the RAM are wiped out automatically when we turn off the switch.
  8. 4Lucky711 👍 3
    ARP (Address Resolution Protocol) is a layer 2 protocol, not a layer 3 protocol. This is because ARP is used to map a network layer 3 (IP) address to a link layer 2 (MAC) address. It operates at the Data Link Layer of the OSI Model, which is the second layer. It is not considered a layer 3 protocol because it does not deal with routing or managing the flow of data at the network layer.
  9. Naaji 👍 3 Answered D
    A switch can learn MAC addresses in two ways; statically or dynamically. In the static option, we manually add MAC addresses to the CAM table. In the dynamic option, the switch automatically learns and adds MAC addresses to the CAM table. Adding MAC addresses to the CAM table is a tedious task.
  10. Sant11 👍 3 Answered D
    A static MAC address entry is indeed manually added to the MAC address table on a switch, and this can be considered a form of MAC address learning.
  11. CCNPTT 👍 3
    Forget about C, it's D. Do your switches have AN ARP table? No.
  12. exiledwl 👍 3 Answered D
    A switch doesn't even have an arp table, Answer D is correct
  13. Jack67 👍 3 Answered D
    D is correct answer
  14. Goena 👍 3 Answered C
    The answer is C.
  15. arenjenkins 👍 3 Answered C
    obious
  16. Starlord2535 👍 2 Answered C
    Let’s say that host A wants to communicate with host B for the first time. Host A knows the IP address of host B, but since this is the first time the two hosts communicate, the hardware (MAC) addresses are not known. Host A uses the ARP process to find out the MAC address of host B. The switch forwards the ARP request out all ports except the port the host A is connected to. Host B receives the ARP request and responds with its MAC address. Host B also learns the MAC address of host A (because host A sent its MAC address in the ARP request). Host C receives the ARP request, but doesn’t respond since the IP address listed in the request is not its own. https://study-ccna.com/how-switches-work/
  17. DevNetAdmin 👍 2
    A function of MAC learning on a switch is to dynamically build and maintain the MAC address table, which maps MAC addresses to the interfaces on the switch. The MAC address table is not used to populate the ARP table, which maps IP addresses to MAC addresses.
  18. PyoJH 👍 2 Answered D
    The answer is D. C can't be the answer because it's definitely not, and adding manually can also belong to 'learning', so the answer is only 'D'..
  19. aklas 👍 2 Answered D
    The MAC address table most definitely does NOT populate the ARP table. The ARP table on a L2 switch is for the SVI management interface only.
  20. 7d040c6 👍 2 Answered D
    D is the only correct statement (on its own). However, it seems like an incorrect answer to the question about MAC learning.
  21. MeysamDavabi 👍 2 Answered D
    ARP is using to map layer 2 address to layer 3 address and the ARP table is not filled with CAM table. D is correct
  22. kishan365 👍 2 Answered D
    The same question has been repeated but with different answers. The previous one had answer C but here its D.
  23. g0dofnub 👍 2 Answered D
    Arp is not a laser 2 protocol Answer is D because static mac addresses are learned by manual input
  24. exiledwl 👍 2
    While ARP includes Mac addresses, it has no relation to the mac address table. D) is correct
  25. a67c04a 👍 2 Answered D
    It´s D. MAC table is not used to populate ARP table.

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