What Is a Function of MAC Learning on a Switch?

Describe switching concepts

Answer Correct answer: D — a static MAC address entry is manually added to the switch's MAC address table, the only factually correct option given.

What is a function of MAC learning on a switch?

MAC address learning is disabled by default on all VLANs.
Frames received for a destination MAC address not listed in the address table are dropped.
The MAC address table is used to populate the ARP table.
A static MAC address is manually added to the MAC table. Correct Answer

Community Insight

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.

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.

Community Discussion (50 comments)

itone333 👍 1 Selected: D

A False. It's usually the opposite B ERRRNT! Wrong it actually floods the remaining ports in a vlan C Nope! ARP is (mostly) a layer 3 process D Ehh.. Makes sence since you are telling the switch what to remember. Static & Dynamic MAC learning uses the source MAC address... unknown destination MAC addresses are flooded, not dropped.

Fakecon 👍 1 Selected: D

Think its wrongly worded its either B or D

MeysamDavabi 👍 2 Selected: 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

CharlieZasv 👍 1

When a switch receives a frame with a destination MAC address not in its table, it will flood the frame out all ports (except the one it came from). If no response is received back to update the MAC address table, the frame is ultimately dropped. So the best answer is B

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?

Portcullis 👍 1

They are not fake, the CCNA is actually written like this. My guess its that its a combination of people having a poor grasp on English as well as them trying to make questions unnecessarily complicated so more people fail the exam and have to pay to retake it. A majority of the exam at this point in time (2025) is a test of your English abilities.

Joshua25 👍 1 Selected: C

Only C is talking about a FUNCTION. All the other options, whether true of false, are not a function.

exiledwl 👍 3 Selected: D

A switch doesn't even have an arp table, Answer D is correct

7d040c6 👍 2 Selected: D

D is the only correct statement (on its own). However, it seems like an incorrect answer to the question about MAC learning.

DominikRWeber 👍 1 Selected: D

it is D

networkcity 👍 2 Selected: D

D answer is correct.

g0dofnub 👍 2 Selected: D

Arp is not a laser 2 protocol Answer is D because static mac addresses are learned by manual input

xplinty666 👍 1 Selected: B

MAC learning on a switch involves dynamically building and maintaining a MAC address table (CAM table) that maps MAC addresses to the ports on which they are learned. This table is used to make forwarding decisions based on destination MAC addresses. If a frame is received for a destination MAC address that is not listed in the MAC address table, the switch will flood the frame out of all ports except the port on which the frame was received. This helps prevent unnecessary flooding of frames within the network

exiledwl 👍 2

While ARP includes Mac addresses, it has no relation to the mac address table. D) is correct

Starlord2535 👍 2 Selected: 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/

Ongmusha 👍 1

The question is asking what is a "function", answer should be "To built CAM table, so that the switch makes an independent forwarding decision based on it. Unless the question is "How a Switch learns the MAC addresses?" then the answer is D.

a67c04a 👍 2 Selected: D

It´s D. MAC table is not used to populate ARP table.

Andu93 👍 2 Selected: C

C it is

dsmitd33 👍 1

There is no such expression as “static learning”. On the other hand, “dynamic learning” is a common term used in IT.

aklas 👍 2 Selected: 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.

PyoJH 👍 2 Selected: 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'..

AbdullahMohammad251 👍 1 Selected: A

By default, MAC address learning is enabled on all interfaces and VLANs on the router. https://content.cisco.com/chapter.sjs?uri=/searchable/chapter/www.cisco.com/content/en/us/td/docs/wireless/mwr_2941_dc/software_config/guide/3_5_1/2941_351_ConfigGuide/mac_lrn.html.xml#:~:text=By%20default%2C%20MAC%20address%20learning,VLANs%20can%20learn%20MAC%20addresses.

NewJeans 👍 4 Selected: 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.

CCNPTT 👍 3

Forget about C, it's D. Do your switches have AN ARP table? No.

Naaji 👍 3 Selected: 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.

Sant11 👍 3 Selected: 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.

BarkingSpider 👍 4 Selected: C

a static MAC is manually assigned, not learned.

kishan365 👍 2 Selected: D

The same question has been repeated but with different answers. The previous one had answer C but here its D.

mda2h 👍 5 Selected: 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

dropspablo 👍 25 Selected: 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.

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.

4aynick 👍 5

arp is 2 layer protocol

Jack67 👍 3 Selected: D

D is correct answer

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.

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.

linuxlife 👍 1

If the switch does not find an entry for the source MAC address, it creates a new entry for this MAC address. An entry contains three pieces of information; the source MAC address, the port or interface on which the frame arrived, and the time when the frame arrived. If the switch finds an entry for the source MAC address, it updates that entry and resets the timer of that specific entry. The switch assigns a separate timer to each entry of the CAM table. This timer is used to age out old entries from the CAM table, allowing room to store new entries. This feature is known as the Aging. Once the CAM table is full, the switch has no place to store any new addresses. Aging resolves this issue by automatically removing the old entries from the CAM table. It keeps the MAC addresses of only those devices that are constantly sending the frames. If any device is not sending the frames, once the timer is expired, it removes the MAC address of that device from the CAM table. In this manner, only the devices that are constantly sending frames remain in the CAM table and the devices that are not sending any frames will eventually be removed from the table.

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.

thomson_johnson 👍 1

no, ARP table is for mapping IPs to MACs, CAM / MAC table is for mapping MACs to interfaces

ricky1802 👍 5 Selected: D

Correct answer is D. MAC table - layer 2 ARP - layer 3

4aynick 👍 1

arp 2 layer protocol

Naghini 👍 4 Selected: 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.

Goena 👍 3 Selected: C

The answer is C.

remoto 👍 2 Selected: C

learning, don't is static

Sara_Yus 👍 2

Isn't it supposed to be the CAM Table?

BakedPotato 👍 1

CAM table, MAC-address table, ARP table, forwarding table... all the same thing.

guisam 👍 1

https://medium.com/@cbitss.sheetal0303/understanding-mac-learning-in-ccna-dc3d81a4979b

bruno0147 👍 1

Reposta D

arenjenkins 👍 3 Selected: C

obious

HennieB 👍 32 Selected: C

The question specifically says LEARNING. A Static MAC is not learned

👍 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.

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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

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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