What Is the Primary Effect of spanning-tree portfast?
Answer
Correct answer: D — spanning-tree portfast minimizes spanning-tree convergence time by skipping the listening and learning states on edge ports.
What is the primary effect of the spanning-tree portfast command?
Community Insight
The question asks for the PRIMARY effect of spanning-tree portfast, and the trap is picking the option that describes an immediate forwarding transition coupled with an incorrect qualifier such as only after a switch reload.
PortFast (edge port) bypasses the listening and learning states so an end-host interface reaches forwarding without the normal 30-second STP delay. This page establishes that the primary effect is minimizing spanning-tree convergence time for that port, making option D the correct choice.
Option B is the most tempting wrong answer: PortFast does move the port straight to forwarding, but B ties that behavior to the switch being reloaded, which misrepresents when the command takes effect — it applies immediately upon configuration and on every subsequent boot.
Community Discussion (63 comments)
Tompoo
👍 1
Selected: B
spanning-tree portfast immediately puts an access/edge port into the forwarding state, allowing an attached end device to communicate without waiting for the normal STP state transitions.
macnoble
👍 1
Selected: B
thats the main and primary effect
Fakecon
👍 1
Selected: B
Going B here
Ludo8431
👍 1
Selected: D
The correct answer is D Because, B "It immediately puts the port into the forwarding state when the switch is reloaded." is what PortFast DO But the EFFECT of PortFast is to minimizes spanning-tree convergence time
ssbipa6
👍 1
Its D, portfast does not put an interface straight into forwarding, it just Minimizes the time from 15 seconds to almost instantly.
Nazi_m
👍 2
Selected: D
The primary effect of the spanning-tree portfast command is to skip the STP listening and learning states and immediately transition the port to the forwarding state, which allows for faster network access for end devices (computers, printers, etc.). This is crucial for reducing the time devices need to communicate on the network when plugged in, but it should only be used on end-device ports, not on switch-to-switch links.
jojolabubu
👍 1
Selected: D
B includes a trick, the switch doesn't need to be reloaded.
sds85
👍 1
Cisco developed three proprietary features that improve STP convergence time: PortFast UplinkFast BackboneFast PortFast provides an additional benefit. Remember that a switch will generate a TCN if a port transitions to a forwarding or blocked state. This is true even if the port connects to a host device, such as a workstation. Thus, powering on or off a workstation will cause TCNs to reach the Root Bridge, which will send out configuration BPDUs in response. Because the switching topology did not technically change, no outage will occur. However, all switches will reduce the CAM aging timer to 15 seconds, thus purging MAC addresses from the table very quickly. This will increase frame flooding and reduce the efficiency and performance. PortFast eliminates this unnecessary BPDU traffic and frame flooding. A TCN will not be generated for state changes on a PortFast-enabled port. Therefore D is right and B is discarded because of the reload argument.
Da_Costa
👍 3
Selected: D
D is more appropriate answer
NewJeans
👍 6
Selected: D
The portfast command does not put the port into the forwarding state when the switch is reloaded. The portfast command takes effect immediately after it is configured on a port, regardless of whether the switch is reloaded or not.
Hanagaki_Shinjiro
👍 2
Selected: D
D is correct
kyleptt
👍 1
No need to reload the switch once you set port Fast the port will forward immediately.
Cynthia2023
👍 5
Selected: B
The "spanning-tree portfast" command is used to configure a port as an edge port, typically for end-user devices like computers or IP phones. When this command is applied to a port, it bypasses the normal Spanning Tree Protocol (STP) listening and learning states and immediately transitions the port to the forwarding state as soon as it's activated or the switch is reloaded. This helps to minimize the time it takes for devices to gain network connectivity after they are powered on or connected to the network. The primary effect of the "spanning-tree portfast" command is to quickly enable the port and put it into the forwarding state to allow network traffic to flow without the delay introduced by the STP convergence process. (D) While portfast can contribute to minimizing spanning-tree convergence time by immediately transitioning ports, the primary effect is not about overall convergence time.
Cynthia2023
👍 1
The "spanning-tree portfast" command is used to configure a port as an edge port, typically for devices that do not participate in Spanning Tree Protocol (STP) such as end-user devices like computers or IP phones.
nzieno
👍 1
D is the correct answer. B is slightly correct however a switch does not need to be reloaded for it to work.
Paul889
👍 2
D is the best answer however, really unfair set of choices
Danishh
👍 2
Selected: D
PortFast is a feature can be used to speed up convergence on ports which are connected to a workstation on a server( which will not cause layer 2 loops) # enable #configure terminal #interface fa0/1 -15 #switchport mode access #spanning-tree portfast #exit TO CHECK SPANNING TREE PORTFAST enabled ports Sw#show running-config
ccna_exam
👍 4
Selected: B
The spanning-tree portfast command immediately puts the port into the forwarding state when the switch is reloaded. So the answer is B. The listening and learning states are bypassed when the spanning-tree portfast command is used. This minimizes the spanning-tree convergence time, which is the time it takes for a switch to detect a topology change and converge to a new spanning-tree topology. BPDU messages are used by the Spanning Tree Protocol (STP) to communicate between switches. The spanning-tree portfast command does not affect BPDU messages. Therefore, the primary effect of the spanning-tree portfast command is to minimize spanning-tree convergence time by immediately putting the port into the forwarding state.
xbololi
👍 1
It asks for effect...
Danishh
👍 1
Portfast feature causes a switch port to enter the spanning tree forwarding state immediately, bypassing the listening and learning states.
VanessaR05
👍 1
Selected: B
https://community.cisco.com/t5/blogs-routing-y-switching/caracter%C3%ADsticas-avanzadas-de-spanningtree-portfast-bpdu-guard-y/ba-p/3104851 PortFast permite que el puerto entre en un estado de Forwarding inmediatamente, pasando por alto los estados Listening y Learning.
Isuzu
👍 2
Selected: B
The primary effect of the "spanning-tree portfast" command is to immediately transition a port from the blocking state to the forwarding state when the switch port is enabled. This is useful for ports that are connected to end devices, such as PCs or servers, which do not participate in the Spanning Tree Protocol (STP) and do not need to wait for the full STP convergence process. Portfast can reduce the time it takes for end devices to get network connectivity and minimize the risk of connectivity issues caused by spanning tree loop avoidance mechanisms. Therefore, option B is the correct answer. Option A is not accurate because the "listening" state is a transient state during the STP convergence process and Portfast does not skip it. Option C is incorrect because Portfast is not related to enabling or disabling BPDU messages. Option D is partially correct, as Portfast can minimize the STP convergence time for the specific ports where it is enabled, but it does not affect the overall STP convergence time.
hamish88
👍 1
When a switch is reloaded means when the STP process kicks in. It is not said we need to reload the switch to have the portfast feature work. The convergence time for STP is 40-50 seconds and for RSTP is 5-10 seconds. Portfast doesn't make them any faster. Finally, we all enable portfast to have a port up and running immediately without having it go through listening, learning, etc states. Don't care if the switch is reloaded, or unplugged, there is a power outage, water damage, earthquake, etc.
jibon_22
👍 1
Look at the words "primary effect". Correct answer is: > B
AppleShredder011
👍 1
The answer is D. Portfast puts interface FROM blocking TO forwarding and not FROM a device restart. B is for Uplinkfast which puts the interface to forwarding right after reloading or a restart.
ZUMY
👍 5
D is correct!
jahinchains
👍 3
Selected: D
there is no need for a switch to be reloaded B is not correct
👍 2
Selected: D
Just pick D and stop thinking so hard on it. If people in India can pass this, so can you lol. Better hurry up and learn cloud stuff and automation, because vanilla IT is going the way of the dinosaurs
bitree
👍 5
People in India have brains primed for memorization from the school system, and probably face economic pressures and levels of cutthroat competition I will never know. People who live in flyover country, USA should not insinuate about people in India to compare to other peoples.
onikafei
👍 2
Selected: D
D is correct
onikafei
👍 1
To further elaborate: A and B are essentially answers for a when you start it up. But its not asking for this in the question, it is asking for the primary effect. so scratch A and B out. Then from there I look primarily on D
Vinarino
👍 1
This Q is reiterated again, omitting "when the switch is reloaded" - THEN D is correct. After entering the command What is your desired (planned) result a week later?
pfwxmneydgygqyhekw
👍 7
"You can use Port Fast on interfaces connected to a single workstation or server to allow those devices to immediately connect to the network, rather than waiting for the spanning tree to converge." This is not the same as reducing spanning tree convergence time.
YessufAddis
👍 4
I believe the answer is B. Portfast is a feature for edge ports and it doesn't have anything to do with spanning-tree convergence. Spanning-tree convergence is the issue of other ports which switches are connected with other switches. Thus, portfast is a feature to bring ports connected to user devices to forwarding states as quick as possible.
ostralo
👍 2
B is wrong hence the answer is D. the spanning-tree portfast command doesn't put whatever ports into forwarding state as soon as the switch is reloaded. normally we configure portfast on ports where end devices are connected to, and along with the BPDU guard.
edward99
👍 2
For my understand,the answer is D since although the port bypass the other states like blocking, listening, learning and go to forwarding states,this led to reduce the converges time the switch may use from blocking to forwarding states
Nhan
👍 4
B is not correct answer, it will put the port to forwarding immediately without switch reload, you can just shut the int and turn the int back on. Therefore the statement B is not correct D is right answer
xsp
👍 1
Answer is B.
hokieman91
👍 2
This is a "gotcha" question since the one statement of "when the switch is reloaded" is a misdirection. Had this line been eliminated, "B" would have been the BEST answer. While this statement could be true, it is not the BEST answer now - going with D. I have heard that many questions will have multiple correct answers but only 1 BEST answer
admin1982
👍 3
I believe the correct answer is D. The reason, port-fast immediately causes the switch to forward traffic...there is no reboot needed, think about the answer (B) it speak about reboot, the question is about the "primary effect" of port-fast, how often does one reboot a switch??? I think you've got the point.
Ali526
👍 2
I chose D, but I must admit that this paragraph in Cisco book can cause confusion: "Port Fast immediately brings an interface configured as an access or trunk port to the forwarding state from a blocking state, bypassing the listening and learning states. You can use Port Fast on interfaces connected to a single workstation or server, as shown in Figure 18-1, to allow those devices to immediately connect to the network, rather than waiting for the spanning tree to converge."
Ali526
👍 2
I'll go with D. The reason is the way B is written: "It immediately puts the port into the forwarding state 'when the switch is reloaded'." The last part of the sentence makes B a wrong answer. When a switch is "reloaded", it does NOT "immediately" go into forwarding state; it does a lot more things and it still goes to "learning" state before settling down in forwarding state. It's possible that the "reloading" part is added on purpose just to make it an incorrect answer.
hamed4maf
👍 2
the correct answer is B Spanning tree port fast caused to speed up convergence on a port, not minimize the spanning-tree convergence time
painkillers
👍 3
I think B is the incorrect answer. The key words are "when the switch is reloaded". The reference site states as "An interface with Port Fast enabled goes through the normal cycle of spanning-tree status changes when the switch is restarted."
promaster
👍 1
Port Fast immediately brings an interface configured as an access or trunk port to the forwarding state from a blocking state, bypassing the listening and learning states.
nar6du14
👍 2
the correct answer is D because it is not necessary to wait the converge to complete before putting switches's port linked to a server or a user's station in the forwarding state
khalid86
👍 2
I also agree that the answer is D.
Ebenezer
👍 4
Well, I think the right answer is D. From the reference the admin added, I saw this - ''Because the purpose of Port Fast is to minimize the time interfaces must wait for spanning-tree to converge, it is effective only when used on interfaces connected to end stations. If you enable Port Fast on an interface connecting to another switch, you risk creating a spanning-tree loop. ''
Package
👍 2
I think D is the correct answer
RexChen
👍 3
Maybe is D, Both B D are right . but it asks "primary effect", primary effect is for convergence time., not to reboot switch
Pras86
👍 1
When the switch powers up, or when a device is connected to a port, the port enters the spanning tree listening state. When the Forward Delay timer expires, the port enters the learning state. When the Forward Delay timer expires a second time, the port is transitioned to the forwarding or blocking state. When you enable PortFast on a switch or trunk port, the port is immediately transitioned to the spanning tree forwarding state. B is correct
Ewaoluwa
👍 2
D is the right answer. Note the question says what is the primary effect. https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst4000/8-2glx/configuration/guide/stp_enha.html
awtkas983
👍 6
if you will understand option B word by word: B. It immediately puts the port into the forwarding state when the switch is reloaded. it means that the changes only takes effect when you reload the switch. So if you will not reload the switch, the configuration will not or never take effect. This opton will be correct if this statement ("when the switch is reloaded") was not added. Best answer is option D
Tidestar
👍 62
I believe D is the right answer. When you enable PortFast on the switch, spanning tree places ports in the forwarding state immediately, instead of going through the listening, learning, and forwarding states. If answer B did not say " when the switch is reloaded" then it would have been the correct answer.
vkv1975
👍 1
B is right answer
iRodimusPrime
👍 4
B is correct - from included reference below: Port Fast immediately brings an interface configured as an access or trunk port to the forwarding state from a blocking state, bypassing the listening and learning states. You can use Port Fast on interfaces connected to a single workstation or server, as shown in Figure 18-1, to allow those devices to immediately connect to the network, rather than waiting for the spanning tree to converge.
Salem2020s
👍 4
as long as Portfast is used for ports connected to end stations, then there is no point to ask about the effects of spanning-tree procces, i think its a tricky qusetion
Tag
👍 24
guys, note, the question asks, what is the "primary" effect. Which would be D
JWMcInSC
👍 5
Agreed: Because the purpose of Port Fast is to minimize the time interfaces must wait for spanning-tree to converge, it is effective only when used on interfaces connected to end stations.
TeeItUp
👍 2
I've seen both B and D as answers on multiple sources, wish there was a straight answer on this one.
akhuseyinoglu
👍 4
Right Answer : B
Samitha
👍 6
Primary effect is D.It skip listen,....and other things.
JWMcInSC
👍 2
I thought the same initially ak but I found this: An interface with Port Fast enabled goes through the normal cycle of spanning-tree status changes when the switch is restarted.
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Expert Analysis
Why the Answer Is Correct
PortFast configures an interface as an STP edge port, so the switch skips the listening and learning states and sends the port directly to forwarding. Because the usual 15-second listening plus 15-second learning delays are eliminated, the interface no longer waits for spanning-tree convergence before carrying traffic — which is precisely what option D states: "It minimizes spanning-tree convergence time." Commenters such as Tag and Samitha reinforced that the word "primary" points at this net timing benefit rather than at a single state transition, and JWMcInSC likewise concluded that "the purpose of Port Fast is to minimize the time interfaces must wait for spanning-tree to converge." Cisco's own documentation frames PortFast as allowing end devices to connect immediately "rather than waiting for the spanning tree to converge."Why the Other Options Are Wrong
Option A is wrong because PortFast does not leave the port in listening — listening is the state it skips entirely; the port goes straight to forwarding. Option B would be nearly correct if it dropped the clause "when the switch is reloaded," but as written it implies the command only works after a reload, whereas NewJeans and awtkas983 correctly observed the command takes effect immediately on configuration and on any reload. Option C is incorrect because PortFast does not enable BPDU messages; edge ports still send and receive BPDUs (and receiving a BPDU on a PortFast port triggers the port to leave edge mode for safety), but enabling BPDUs is not the command's function. Option D best captures the overall consequence of skipping two timer states.Community Comment Notes
The comment thread converges on D, with Tidestar explaining that PortFast places ports in forwarding "instead of going through the listening, learning, and forwarding states" and explicitly rejecting B because of the reload qualifier. pfwxmneydgygqyhekw quoted Cisco's wording that PortFast lets devices "immediately connect to the network" and argued this is not literally the same as shrinking the STP convergence algorithm — a fair nuance, but the exam-style intent still favors the convergence-time answer. Cynthia2023 alone argued for B, grounding the claim in activation "or when the switch is reloaded," which is the minority position. One comment from bitree drifted entirely away from the topic into cultural remarks and carries no technical value for this question.Official Reference
Exam Strategy
Read the qualifier words carefully — a single clause like "when the switch is reloaded" can invalidate an otherwise plausible option, and when a question asks for the "primary" effect it wants the broad operational benefit, not one narrow step in the process.
Frequently Asked Questions
Why is "immediately puts the port into forwarding when the switch is reloaded" not the right answer?
Because the wording ties the behavior to a reload, implying the command does nothing until the switch restarts. PortFast takes effect immediately after configuration and on every boot, so the qualifier makes option B incorrect.
Does spanning-tree portfast enable BPDU messages on the port?
No. PortFast changes only the state-transition timing; the port still sends and receives BPDUs, and receiving a BPDU on a PortFast edge port causes it to fall back to normal STP behavior.
Should PortFast be used on links between switches?
No. PortFast belongs only on access ports facing end stations such as PCs, phones, or servers; applying it to a trunk toward another switch risks creating a Layer 2 loop.
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