The answer is the show interfaces transceiver command, because it directly reveals the SFP type mismatch causing link flapping by displaying optical parameters like transmit and receive power levels. When a 10GBASE-SR multimode module is paired with a 10GBASE-LR single-mode module over 500 meters, the signal degrades beyond the SR’s 300-meter limit, triggering excessive attenuation and the 'Link error recovery - will restart' flapping. On the CCNA 200-301 v2 exam, this tests your ability to diagnose physical-layer issues using show interfaces transceiver, a key troubleshooting command often overshadowed by show interfaces status. A common trap is assuming the link distance alone is the problem, but the command confirms the root cause by showing abnormally low receive power or a transceiver type mismatch. Memory tip: think "SFP flapping? Check the transceiver stats—power tells the story."
CCNA Network Infrastructure and Connectivity Practice Question
This 200-301 practice question tests your understanding of network infrastructure and connectivity. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
Exhibit
SwitchA# show interfaces gigabitethernet1/0/1 transceiver
Diagnostic Monitoring Information:
Temperature: 45.2°C
Voltage: 3.3 V
Current: 10.5 mA
Output Power: 0.5 mW
Input Power: 0.2 mW
Laser Bias: 12.0 mA
SwitchA# show interfaces gigabitethernet1/0/1 | include errors
5 minute input rate 1002000 bits/sec, 200 packets/sec
5 minute output rate 1005000 bits/sec, 210 packets/sec
Input errors: 0, CRC errors: 0, Frame errors: 0
Output errors: 0, Collisions: 0
SwitchA# show interfaces gigabitethernet1/0/1
GigabitEthernet1/0/1 is up, line protocol is up (err-disabled)
Hardware is Gigabit Ethernet, address is aaaa.bbbb.cccc
MTU 1500 bytes, BW 1000000 Kbit/sec
Full-duplex, 1000Mb/s
input flow-control is off, output flow-control is off
Last input never, output never, output hang never
Last clearing of "show interface" counters never
Input queue: 0/2000/0/0 (size/max/drops/flushes); Total output drops: 0
Queueing strategy: fifo
Output queue: 0/40 (size/max)
5 minute input rate 0 bits/sec, 0 packets/sec
5 minute output rate 0 bits/sec, 0 packets/sec
0 packets input, 0 bytes, 0 no buffer
Received 0 broadcasts (0 IP multicasts)
0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
0 watchdog, 0 multicast, 0 pause input
0 input packets with dribble condition detected
0 packets output, 0 bytes, 0 underruns
0 output errors, 0 collisions, 0 interface resets
0 unknown protocol drops
0 babbles, 0 late collision, 0 deferred
0 lost carrier, 0 no carrier, 0 pause output
0 output buffer failures, 0 output buffers swapped out
SwitchA# show logging | include SFP
%PHY-4-UNSUPPORTED_TRANSCEIVER: Unsupported transceiver found in Gi1/0/1
%PM-4-ERR_DISABLE: link-flap error detected on Gi1/0/1, putting Gi1/0/1 in err-disable state
A network engineer notices that a critical link between two Cisco Catalyst 9300 switches is flapping every few minutes. The link uses a 10GBASE-SR SFP+ module on one end and a 10GBASE-LR SFP+ module on the other. The interface logs show 'Link error recovery - will restart'. The distance between the switches is 500 meters. Which command output best confirms the root cause of the flapping?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "best"
Why it matters: Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
Clue: "which command"
Why it matters: Tests specific CLI syntax. Recall the exact command and its required context — near-synonyms and partial matches are common distractors.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
show interfaces transceiver
The correct answer is B because the 'show interfaces transceiver' command displays the optical parameters (e.g., transmit power, receive power, temperature) of the SFP+ modules. The mismatch between a 10GBASE-SR (multimode, 300m max) and a 10GBASE-LR (single-mode, 10km max) over 500 meters causes excessive attenuation and signal loss, triggering the 'Link error recovery - will restart' flapping. This command confirms the root cause by showing abnormal receive power levels or a missing/different transceiver type.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
show interfaces status
Why it's wrong here
This command shows interface status and errors but does not provide transceiver-specific details.
✓
show interfaces transceiver
Why this is correct
This command displays the transceiver type, diagnostic monitoring, and can confirm the SFP+ mismatch (e.g., 10GBASE-SR vs 10GBASE-LR).
Clue confirmation
The clue words "best", "which command" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
show interfaces gigabitethernet1/0/1
Why it's wrong here
This shows the interface status and errors but does not reveal the transceiver type.
✗
show logging
Why it's wrong here
This shows log messages including the unsupported transceiver warning, but does not directly confirm the transceiver type mismatch.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The 200-301 exam frequently reuses these exact scenarios with slightly different constraints.
✓show interfaces transceiverCorrect answer▾
Why this is correct
This command displays the transceiver type, diagnostic monitoring, and can confirm the SFP+ mismatch (e.g., 10GBASE-SR vs 10GBASE-LR).
✗show interfaces statusWrong answer — click to see why▾
Why this is wrong here
It does not show the transceiver type or diagnostic information.
✗show interfaces gigabitethernet1/0/1Wrong answer — click to see why▾
Why this is wrong here
It only shows the interface is err-disabled due to link-flap, not the root cause.
✗show loggingWrong answer — click to see why▾
Why this is wrong here
It indicates a problem but does not provide the specific transceiver details.
Analysis generated from the official 200-301blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the distinction between symptom-identifying commands (like 'show logging') and root-cause-identifying commands (like 'show interfaces transceiver'), trapping candidates who stop at seeing the error message without investigating the physical layer mismatch.
Trap categories for this question
Command / output trap
This command shows interface status and errors but does not provide transceiver-specific details.
Detailed technical explanation
How to think about this question
10GBASE-SR (short-range) uses 850nm wavelength over multimode fiber (OM3/OM4) with a maximum distance of 300m, while 10GBASE-LR (long-range) uses 1310nm over single-mode fiber with a reach of 10km. Mixing these modules forces the link to operate over a single-mode fiber (if that's the installed cable) but with an SR transmitter that cannot drive the signal 500m, resulting in a receive power below the LR receiver's sensitivity threshold (typically -14.4 dBm), causing continuous link flaps. The 'show interfaces transceiver' command reveals the actual optical power levels and the transceiver type (e.g., '10GBASE-SR' vs '10GBASE-LR'), directly identifying the mismatch.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A practitioner preparing for the 200-301 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 200-301 question in full detail.
Network Infrastructure and Connectivity — This question tests Network Infrastructure and Connectivity — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: show interfaces transceiver — The correct answer is B because the 'show interfaces transceiver' command displays the optical parameters (e.g., transmit power, receive power, temperature) of the SFP+ modules. The mismatch between a 10GBASE-SR (multimode, 300m max) and a 10GBASE-LR (single-mode, 10km max) over 500 meters causes excessive attenuation and signal loss, triggering the 'Link error recovery - will restart' flapping. This command confirms the root cause by showing abnormal receive power levels or a missing/different transceiver type.
What should I do if I get this 200-301 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "best", "which command". Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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