Which PoE Mode Guarantees Power After Device Detection?
Explain the role and function of network components
Describe physical infrastructure connections of WLAN components (AP, WLC, access/trunk ports, and LAG)
Answer
Correct answer: B — static mode enables powered-device detection and pre-allocates power, guaranteeing it will be provided when a device is detected.
Which PoE mode enables powered-devices detection and guarantees power when the device detected?
Community Insight
The question tests whether you can distinguish Cisco's auto and static PoE port modes; the trap is seeing 'powered-device detection' and picking auto, while the keyword 'guarantees' points to static's pre-allocated power reservation.
Cisco Catalyst switches offer PoE port modes (auto and static) that both enable powered-device detection, but only one pre-allocates power so it is guaranteed on detection. This page establishes that static mode is the correct answer because it reserves wattage in advance, while auto mode grants power first-come, first-served.
Choosing A (auto) is the most common error: auto does enable detection, but it only allocates power if budget remains at that moment, so a detected device is not guaranteed power when other ports consumed the budget first.
Community Discussion (71 comments)
carlalap
👍 1
Selected: B
B. is correct. It is a confusing question. Both Enables powered-device detection, but the key different is: Static — Enables powered-device detection; pre-allocates (reserves) power for a port... and guarantees that power will be provided upon device detection. Auto - doesn't guarantee power if all ports on the switch are fully utilizing the power budget.
d11eb6d
👍 1
Selected: B
B is correct.
Portcullis
👍 1
Selected: A
The correct PoE mode that enables powered-device (PD) detection and guarantees power once the device is detected is auto. In auto mode, the switch port actively detects if a powered device (like an IP phone or camera) is connected, and if so, it supplies power accordingly, meeting the requirement of detection and guaranteed power after detection. While static mode also guarantees power, it forces power on the port whether a device is detected or not, which isn't aligned with the question's emphasis on detection. Dynamic and active are not standard PoE modes in Cisco terminology. Therefore, auto is the best fit for the described behavior.
JRossJ
👍 1
Your ChatGPT answer is wrong though. It says "GUARANTEES" power, which would be static. Auto will only give it power if its available. Static will give it power regardless.
d0cca29
👍 2
Selected: A
In auto mode, the switch automatically detects the presence of a powered device and provides the appropriate amount of power to it. This ensures that power is supplied only when a compatible device is connected, and the power delivery is managed efficiently.
nadamos
👍 4
Selected: B
It's important to note that while the auto mode also enables powered-device detection, it does not guarantee power in the same way that static mode does
JRossJ
👍 1
Its worded poorly, it is static. Static still requires detection - it sends pulses to detect if the device is POE compatible.
Steve14
👍 2
Selected: B
https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst9400/software/release/16-9/configuration_guide/int_hw/b_169_int_and_hw_9400_cg/configuring_poe.html
jojolabubu
👍 2
Selected: B
Would go for B, Auto and Static detect the device, only Static guarantees the power delivery.
jojolabubu
👍 2
I correct myself, A (Auto) as Static doesn't involve detection.
RahmNn
👍 2
Selected: A
A. auto Explanation: Auto Mode: In Power over Ethernet (PoE), auto mode allows for the detection of powered devices (PDs) connected to the PoE switch or injector. When a device is detected, the PoE switch negotiates and guarantees the appropriate amount of power for that device. This mode ensures that power is supplied only to devices that require it and are capable of using it, helping to prevent power wastage and potential overloads.
Doman01
👍 2
According to this: https://www.cisco.com/en/US/docs/switches/lan/catalyst3850/software/release/3.2_0_se/multibook/configuration_guide/b_consolidated_config_guide_3850_chapter_011010.html Answer is AUTO Configures the PoE mode on the port. The keywords have these meanings: auto—Enables powered-device detection. If enough power is available, automatically allocates power to the PoE port after device detection. This is the default setting. never —Disables device detection, and disable power to the port. Note If a port has a Cisco powered device connected to it, do not use the power inline never command to configure the port. A false link-up can occur, placing the port into the error-disabled state. static—Enables powered-device detection. Pre-allocate (reserve) power for a port before the switch discovers the powered device. The switch reserves power for this port even when no device is connected and guarantees that power will be provided upon device detection.
TrueLearner
👍 3
Selected: A
auto—The switch automatically detects if the connected device requires power. If the switch discovers a powered device connected to the port and if the switch has enough power, it grants power, updates the power budget, turns on power to the port on a first-come, first-served basis, and updates the LEDs
scanossa
👍 1
Selected: B
static : The device preallocates power to the port (even when no powered device is connected) and guarantees that power will be available for the port. https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst9400/software/release/17-11/configuration_guide/int_hw/b_1711_int_and_hw_9400_cg/configuring_poe.html#:~:text=Cisco%20Universal%20Power%20Over%20Ethernet%20(Cisco%20UPOE)%20is%20a%20Cisco,%2C7%2C8)%20with%20the
vinbra
👍 1
"powered-devices detection" you misseed that part
xtraMiles
👍 1
Selected: B
I initially picked A without hesitation. The definition is so closely similar on Cisco's site. But, after further reading, I noticed Cisco (and perhaps other brands as well) prefers "static" and prioritizes it over a port that is configured w/ "auto". This seems to be a pattern with other networking concepts as well like in EtherChannel/LAG, where you stay away from "auto" if possible. Although, I don't think we ever configured any of our switches at work w/ "static". I can see how this might actually pose some issues at work though. New techs might mistake a client's equipment as broken from shipment if this ever happened in shared colocations where multiple clients/servers are on the same switch and the newly arrive equipment does not lit up after connecting a cable to a switch port. Anyhow, good reading I suppose.
cybercerberes
👍 3
Selected: A
See in google search, the cisco site explain....Correct answer is A (Auto)
1b81c0c
👍 1
Selected: B
More B than A
rodrigocalcarao
👍 2
Selected: B
https://www.cisco.com/en/US/docs/switches/lan/catalyst3850/software/release/3.2_0_se/multibook/configuration_guide/b_consolidated_config_guide_3850_chapter_011010.html#:~:text=static%E2%80%94Enables%20powered%2Ddevice%20detection.%20Pre%2Dallocate%20(reserve)%20power%20for%20a%20port%20before%20the%20switch%20discovers%20the%20powered%20device.%20The%20switch%20reserves%20power%20for%20this%20port%20even%20when%20no%20device%20is%20connected%20and%20guarantees%20that%20power%20will%20be%20provided%20upon%20device%20detection.
Harsh2729
👍 2
Answer is A because its written that "enables devices" and detection. Static will always provide power even is the device is plugged or not. Auto detects the poe enabled devices and send power.
VanessaR05
👍 3
Selected: B
It is static, key word is "guarantees"
vktsupport
👍 3
Selected: B
The question said: guarantees power when the device detected? It is answer B - Static Go to index - Power Management Modes. Then, at the end of the Static description, it said: Use the static setting on a high-priority interface. Source: https://www.cisco.com/en/US/docs/switches/lan/catalyst3850/software/release/3.2_0_se/multibook/configuration_guide/b_consolidated_config_guide_3850_chapter_011010.html#con_1874624
Da_Costa
👍 2
Selected: B
It is static
Cyber15
👍 2
B. static
AbdullahMohammad251
👍 3
Selected: B
The switch allocates power to a port configured in static mode before it allocates power to a port configured in auto mode. This means if we have limited power and 2 devices we connect to the switch at the same time with one port set to auto mode and the other set to static, The static port will guarantee power since it's served first but the auto port wouldn't if we ran out of power. So, I think it's static. https://www.thinlabs.com/faq/configure-cisco-switch-for-powering-poe-client#:~:text=static%20%2D%20Enables%20powered%2Ddevice%20detection,be%20provided%20upon%20device%20detection.
syougun200x
👍 1
But the question says about power detection. Why do we have to not select the mode with power detection and create a scenario that lacks what is required in the question? Anything am i missing here. why Q. Which PoE mode enables powered-devices detection and guarantees power when the device detected?
Da_Costa
👍 2
Selected: B
static
Da_Costa
👍 2
Selected: B
Static not auto
ZK23
👍 2
Copy the question and paste it on google search. The answer is auto. The first link is Cisco's answer.
SAAVYTECH
👍 3
A. Auto In Power over Ethernet (PoE) terminology, "auto" mode, also known as "auto-detect" or "auto-sensing" mode, enables powered device detection and guarantees power when a compatible device is detected. When a device is connected to a PoE switch or injector configured in auto mode, it will check whether the connected device is PoE-compatible and supply power accordingly. If a PoE-compatible device is detected, the switch will provide power to it. If the connected device is not PoE-compatible, power will not be supplied, ensuring that non-PoE devices are not damaged.
Aymen91
👍 2
Selected: A
auto - Enables powered-device detection; if enough power is available, automatically allocates power to the PoE port after device detection (default setting). static - Enables powered-device detection; pre-allocate (reserve) power for a port before the switch discovers the powered device; the switch reserves power for this port even when no device is connected and guarantees that power will be provided upon device detection in the question, is saying when device is detected and not before even detecting device so Auto is correct
lofidawg
👍 3
Selected: B
"static—Enables powered-device detection. Pre-allocate (reserve) power for a port before the switch discovers the powered device. The switch reserves power for this port even when no device is connected and guarantees that power will be provided upon device detection." https://www.cisco.com/en/US/docs/switches/lan/catalyst3850/software/release/3.2_0_se/multibook/configuration_guide/b_consolidated_config_guide_3850_chapter_011010.html
Da_Costa
👍 2
Selected: B
B is right
Da_Costa
👍 2
Selected: B
B is correct
MonsieurP
👍 1
B is correct, not A Refer to Cisco documentation titled "Configuring PoE"
Da_Costa
👍 3
Selected: B
Static is the correct answer
Yinxs
👍 3
Selected: B
The key word is "guarantee". A. auto mode can't guarantee, if enough power is available, the connected device can get the power. B. static mode can pre-allocate the power, so it can guarantee the power to the device.
MauroC19
👍 1
Selected: A
Key word is "detection". For me, the correct answer is A Check: https://www.cisco.com/en/US/docs/switches/lan/catalyst3850/software/release/3.2_0_se/multibook/configuration_guide/b_consolidated_config_guide_3850_chapter_011010.html
Elmasquentona963
👍 2
Not my friend, the key word is "guarantees". So the answer is B.
Bili123
👍 1
What is the correct answer?
Elmasquentona963
👍 1
It's B.
akareem999
👍 2
Selected: B
Answer is B static—Enables powered-device detection. Pre-allocate (reserve) power for a port before the switch discovers the powered device. https://www.cisco.com/en/US/docs/switches/lan/catalyst3850/software/release/3.2_0_se/multibook/configuration_guide/b_consolidated_config_guide_3850_chapter_011010.html#:~:text=static%E2%80%94Enables%20powered%2Ddevice%20detection,switch%20discovers%20the%20powered%20device.
zFlyingLotusz
👍 1
Everyone... Everyone... It's D, Active. For those who think "Static" has detection is wrong. The question states it requires gurenteed power and device detection, and the only one that provides both is Active. Auto does not guarantee power if another port is allocated to Active. Static does not have device detection.
zFlyingLotusz
👍 1
Everyone... Everyone... It's D, Active. For those who think "Static" has detection is wrong. The question states it requires guaranteed power and device detection, and the only one that provides both is Active.
Natalie89
👍 2
Selected: B
static - Enables powered-device detection; pre-allocate (reserve) power for a port before the switch discovers the powered device; the switch reserves power for this port even when no device is connected and guarantees that power will be provided upon device detection
xbololi
👍 2
Selected: B
Configures the PoE mode on the port. Keywords and meanings: auto - Enables powered-device detection; ""if enough power is available"", automatically allocates power to the PoE port after device detection (default setting). static - Enables powered-device detection; pre-allocate (reserve) power for a port before the switch discovers the powered device; the switch reserves power for this port even when no device is connected and guarantees that power will be provided upon device detection. "if enough power is available" means its not a guarenteed method as the question... So definetly not Auto... " the switch reserves power for this port even when no device is connected and guarantees that power" this is guarenteed method. https://www.thinlabs.com/faq/configure-cisco-switch-for-powering-poe-client#:~:text=static%20%2D%20Enables%20powered%2Ddevice%20detection,be%20provided%20upon%20device%20detection.
VanessaR05
👍 3
Selected: B
https://www.cisco.com/en/US/docs/switches/lan/catalyst3850/software/release/3.2_0_se/multibook/configuration_guide/b_consolidated_config_guide_3850_chapter_011010.html#:~:text=static%E2%80%94Enables%20powered%2Ddevice%20detection,be%20provided%20upon%20device%20detection. static—Enables powered-device detection. Pre-allocate (reserve) power for a port before the switch discovers the powered device. The switch reserves power for this port even when no device is connected and guarantees that power will be provided upon device detection.
dropspablo
👍 1
Correction (after looking at your link) the right answer is the letter B. static. Because in fact the mode that doesn't detect it would just be the "never mode", because all the others detect the device's PoE. But if a port with dynamic or auto mode loses connection and another device fills the power gap (as plug-and-play works, auto mode is the default), that port may no longer have power on the switch because another device got ahead, which is risky and not offering a guarantee of power. Only with static mode can we guarantee that a pre-established energy reserve will always fully serve this port, when there is a need, according to the configured maximum watts. Thank you kyleptt!
Danishh
👍 2
static—Enables powered-device detection. Pre-allocate (reserve) power for a port before the switch discovers the powered device. The switch reserves power for this port even when no device is connected and guarantees that power will be provided upon device detection.
JJY888
👍 1
It's a bit unethical to put the term auto-detect and it is intentionally misleading. Auto mode will detect the device's power specs but cannot guarantee power. Static mode will detect the device power specs and guarantee power. Typical Cisco question. I have to go with B.
TR3Y
👍 3
Selected: B
From this cisco site itself. Please correct me if I am wrong. The definition has the same wording as the question. "Guarantees power will be available upon detection." https://www.cisco.com/en/US/docs/switches/lan/catalyst3850/software/release/3.2_0_se/multibook/configuration_guide/b_consolidated_config_guide_3850_chapter_011010.html
Isuzu
👍 2
Selected: A
The PoE mode that enables powered-devices detection and guarantees power when the device detected is "auto" mode. In "auto" mode, the Power Sourcing Equipment (PSE) detects the powered device (PD) before providing power, and then delivers the appropriate power level to the PD. If the PD is not detected, or if it is not compatible with the PSE, no power is supplied. This ensures that only compatible devices receive power, and that the appropriate power level is delivered to them.
kyleptt
👍 2
https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst9400/software/release/16-11/configuration_guide/int_hw/b_1611_int_and_hw_9400_cg/configuring_poe.html#:~:text=The%20device%20supports%20these%20PoE%20modes%3A%201%20auto,even%20if%20an%20unpowered%20device%20is%20connected.%20
dropspablo
👍 3
Selected: A
Answer A, because there are three configuration modes in PoE, Static, Auto and Dynamic. The three modes CAN guarantee the power. But only Auto and Dynamic modes DETECT the device (along with the required power). And the Dynamic mode, in addition to guaranteeing energy, detecting the device, it also NEGOTIATES energy, because if the switch has less watts to supply, it can partially feed the device. As it was only asked in the question to GUARANTEE the energy and DETECT the device, the Auto mode already answers (Answer A). If it asked to also "negotiate", it would have to be Dynamic mode. Static mode is wrong as it cannot detect the device, it just guarantees power. And Active mode does not exist in the configuration.
dropspablo
👍 1
Example: Switch(config-if)# power inline static max 15400 Switch(config-if)# power inline auto max 15400 Switch(config-if)# power inline dynamic max 30000 The MAX keyword defines the maximum amount of power that can be supplied to the device. In these examples, we have the maximum power 15400 as 15.4 watts and 30000 as 30 watts. Some switches may use a different keyword for dynamic mode, such as "auto-max".
country_rooted
👍 1
STATIC guarantees power when the device is connected AUTO will only provide power if it is available Ans=B
DL86
👍 5
Selected: B
B, keyword is guarantees power. Auto does not guarantees, static does.
BATSIE
👍 26
auto - Enables powered-device detection; if enough power is available, automatically allocates power to the PoE port after device detection (default setting). max max-wattage - limits the power allowed on the port; if no value is specified, the maximum is allowed. max max-wattage - limits the power allowed on the port; range is 4000 to 30000 mW; if no value is specified, the maximum is allowed. never - disables device detection, and disable power to the port. Note: If a port has a Cisco powered device connected to it, do not use the power inline never command to configure the port. A false link-up can occur, placing the port into the error-disabled state. static - Enables powered-device detection; pre-allocate (reserve) power for a port before the switch discovers the powered device; the switch reserves power for this port even when no device is connected and guarantees that power will be provided upon device detection. The switch allocates power to a port configured in static mode before it allocates power to a port configured in auto mode.
enehana_777
👍 3
auto mode —The switch automatically detects if the connected device requires power. If the switch discovers a powered device connected to the port and if the switch has enough power, it grants power, updates the power budget, turns on power to the port on a first-come, first-served basis, and updates the LEDs. For LED information, see the hardware installation guide. If the switch has enough power for all the powered devices, they all come up. If enough power is available for all powered devices connected to the switch, power is turned on to all devices.
enehana_777
👍 2
Auto mode
tonye1OO
👍 1
Selected: D
Active PoE, short for active Power over Ethernet, is also known as standard PoE which refers to any type of PoE that negotiates the proper voltage between the power supply equipment (PSE) and the PD device.
tonye1OO
👍 3
sorry i am wrong, correct answer is A
arenjenkins
👍 1
Selected: A
static : The device pre-allocates power to the port (even when no powered device is connected)
khaledsh00
👍 4
Selected: B
static static—Enables powered-device detection. Pre-allocate (reserve) power for a port before the switch discovers the powered device. The switch reserves power for this port even when no device is connected and guarantees that power will be provided upon device detection.
RougePotatoe
👍 5
Selected: B
Static reserves power and guarantees its availability when it detects a device that requires PoE is connected. Auto does NOT guarantee the availability of power. Auto is first come first serve static is pre-allocated. "Because power is pre-allocated, any powered device that uses less than or equal to the maximum wattage is guaranteed to be powered when it is connected to the static port...The device powers the port only if it discovers a powered device. Use the static setting on a high-priority interface." https://content.cisco.com/chapter.sjs?uri=/searchable/chapter/content/en/us/td/docs/switches/lan/catalyst9200/software/release/16-12/configuration_guide/int_hw/b_1612_int_and_hw_9200_cg/configuring_poe.html.xml#id_114542
dendentester
👍 1
auto - Enables powered-device detection; if enough power is available, automatically allocates power to the PoE port after device detection (default setting).
dendentester
👍 2
static - Enables powered-device detection; pre-allocate (reserve) power for a port before the switch discovers the powered device; the switch reserves power for this port even when no device is connected and guarantees that power will be provided upon device detection.
mhayek
👍 3
Selected: A
A is the correct answer. Keyword is "when". Static provides power even when device is NOT detected.
RougePotatoe
👍 2
Static reserves power and guarantees its availability when a device that requires PoE is connected. Auto does NOT guarantee the availability of power. Auto is first come first serve static is pre-allocated. "Because power is pre-allocated, any powered device that uses less than or equal to the maximum wattage is guaranteed to be powered when it is connected to the static port." https://content.cisco.com/chapter.sjs?uri=/searchable/chapter/content/en/us/td/docs/switches/lan/catalyst9200/software/release/16-12/configuration_guide/int_hw/b_1612_int_and_hw_9200_cg/configuring_poe.html.xml#id_114542
splashy
👍 5
keyword is "guarantees" auto : Enables powered-device detection. If enough power is available, automatically allocates power to the PoE port after device detection. This is the default setting. static : Enables powered-device detection. Pre-allocate (reserve) power for a port before the device discovers the powered device. The device reserves power for this port even when no device is connected and guarantees that power will be provided upon device detection. Static does not provide/allocate power, it pre-allocates/reserves it. The power is reserved (will not be spent on anything else) and only applied to port after device detection.
splashy
👍 6
Selected: B
https://content.cisco.com/chapter.sjs?uri=/searchable/chapter/content/en/us/td/docs/switches/lan/catalyst9200/software/release/16-12/configuration_guide/int_hw/b_1612_int_and_hw_9200_cg/configuring_poe.html.xml#id_114542
Comments & Corrections
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Expert Analysis
Why the Answer Is Correct
Cisco's Catalyst configuration guides define static mode as enabling powered-device detection while pre-allocating (reserving) power for the port before discovery, and the switch "reserves power for this port even when no device is connected and guarantees that power will be provided upon device detection." Because wattage is already committed, any powered device drawing less than or equal to the configured maximum wattage is guaranteed to boot when connected. The question's decisive phrase is "guarantees power," which maps exactly to this static pre-allocation behavior. Community contributors DL86, RougePotatoe, khaledsh00, and VanessaR05 all converged on B for precisely this reason, with RougePotatoe quoting the Cisco wording verbatim. Thus static (B) is the only mode that both detects powered devices and commits power ahead of time.Why the Other Options Are Wrong
Option A (auto) is the tempting distractor and the mode most learners select: it does enable powered-device detection, but Cisco documents it as granting power on a first-come, first-served basis only "if enough power is available," so no guarantee exists once the power budget is exhausted. Options C (dynamic) and D (active) are not valid Cisco PoE port-mode names at all; dynamic PoE terminology belongs to allocation schemes like IEEE 802.3at dynamic power negotiation, not to the switch port mode setting, and "active" is a fabricated distractor here. As TrueLearner and cybercerberes argued for A, their quoted text itself contains the giveaway phrase "first-come, first-served," which contradicts a guarantee. Since the stem explicitly asks for detection plus guaranteed power, auto, dynamic, and active all fail the second half of the requirement.Community Comment Notes
The comments split almost evenly between A and B, but the B side anchored itself in vendor documentation rather than intuition. DL86 captured the logic concisely: "B, keyword is guarantees power. Auto does not guarantees, static does." RougePotatoe reinforced this by noting that "static reserves power and guarantees its availability" and that "Auto is first come first serve," supported by the official Catalyst 9200 PoE guide. Nadamos added the nuance that auto "does not guarantee power in the same way that static mode does," which is the exact distinction the stem tests. On the A side, cybercerberes asserted "See in google search, the cisco site explain....Correct answer is A (Auto)," but the Cisco text quoted by TrueLearner actually describes auto as granting power only when the switch "has enough power," confirming rather than refuting the static verdict.Official Reference
Exam Strategy
On CCNA PoE questions, isolate the exact guarantee keyword: 'guarantee,' 'reserve,' or 'pre-allocate' always points to static mode, while 'first-come, first-served' or 'if enough power is available' points to auto. Remember that both modes perform powered-device detection, so detection alone never distinguishes them.
Frequently Asked Questions
Why is auto mode wrong if it also performs powered-device detection?
Auto grants power only if budget remains, on a first-come, first-served basis. Because nothing is reserved, a detected device can be denied power, so auto fails the 'guarantees' requirement.
What does static PoE mode reserve power for?
Static mode pre-allocates the configured wattage for the port even with no device attached, so any powered device drawing at or below that maximum is guaranteed to power up on connection.
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