Question 1hardmultiple choice
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Question 986 of 1,052
hardmultiple choiceObjective-mapped
CCNA Practice Question: Is troubleshooting a link between two Cisco…
This 200-301 practice question tests your understanding of 200-301 exam topics. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 Gi1/0/1
GigabitEthernet1/0/1 is up, line protocol is up
Hardware is Gigabit Ethernet, address is aabb.ccdd.0001 (bia aabb.ccdd.0001)
Description: Link to SwitchB
Internet address is 192.168.1.1/30
MTU 1500 bytes, BW 1000000 Kbit/sec, DLY 10 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation ARPA, loopback not set
Keepalive set (10 sec)
Full-duplex, 1000Mb/s, media type is 10Gbase-SR
input flow-control is off, output flow-control is off
ARP type: ARPA, ARP Timeout 04:00:00
Last input 00:00:00, output 00:00:00, 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 1000 bits/sec, 1 packets/sec
5 minute output rate 1000 bits/sec, 1 packets/sec
123456 packets input, 12345678 bytes
Received 1200 broadcasts (0 multicast)
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
123456 packets output, 12345678 bytes, 0 underruns
0 output errors, 0 collisions, 1 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 interfaces Gi1/0/1 transceiver details
Diagnostic Monitoring: Yes
Temperature: 45.2 C
Voltage: 3.29 V
Current: 12.5 mA
Output Power: -2.3 dBm
Receive Power: -15.1 dBm
Transmit Fault: No
LOS: No
Nominal bit rate: 10300 Mbps
Connector type: LC
Wavelength: 850 nm
Distance: 300 m
Vendor: CISCO
Part Number: SFP-10G-SR
Serial Number: FNS1234567A network engineer is troubleshooting a link between two Cisco Catalyst 9300 switches that are connected via a 10GBASE-SR SFP+ module on each end over OM3 multimode fiber. The link is up, but the interface counters show a high number of CRC errors and runts. The engineer runs 'show interfaces Gi1/0/1' and 'show interfaces Gi1/0/1 transceiver details'. What is the most likely cause of the errors?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"most likely"Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The receive optical power is too low, indicating a fiber or connector issue.
The 'show interfaces' output shows 0 input errors and 0 CRC errors, but the symptom states high CRC errors—this indicates the exhibit is a red herring. However, the 'show interfaces transceiver details' reveals that the receive power is -15.1 dBm, which is below the typical receive sensitivity threshold for 10GBASE-SR (around -12.6 dBm). This low received optical power causes bit errors, which manifest as CRC errors and runts. The transmit power (-2.3 dBm) is normal, so the issue is likely a degraded fiber or dirty connector, not a faulty SFP.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The SFP+ module is faulty and needs replacement.
Why it's wrong here
The SFP+ module is operating within normal parameters (temperature, voltage, current) and has no transmit fault or LOS. The low receive power is likely due to fiber issues, not a module fault.
- ✗
The fiber patch cables are too long, exceeding the 300-meter distance limit for 10GBASE-SR over OM3 fiber.
Why it's wrong here
The exhibit shows the distance as 300 m, which is the maximum for 10GBASE-SR over OM3 fiber. While this is at the limit, the low receive power (-15.1 dBm) suggests excessive loss beyond the expected 2.6 dB over 300 m, indicating a problem with the fiber or connectors.
- ✗
The interface speed is mismatched; the switch interface shows 1000Mb/s but the SFP+ is 10GBASE-SR.
Why it's wrong here
Although the interface shows 1000Mb/s, this is because the switch is using a GigabitEthernet interface (Gi1/0/1) that is connected via a 10GBASE-SR SFP+. The SFP+ supports 10 Gbps, but the interface is a GigabitEthernet port, so the actual speed is 1 Gbps, not 10 Gbps. However, this mismatch does not cause CRC errors; the link is up and running at 1 Gbps.
- ✓
The receive optical power is too low, indicating a fiber or connector issue.
Why this is correct
The receive power of -15.1 dBm is below the typical receive sensitivity for 10GBASE-SR (about -12.6 dBm). This causes bit errors that appear as CRC errors and runts. The transmit power is normal, so the issue is on the receive side, likely dirty connectors or a damaged fiber.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Static NAT maps one inside address to one outside address.
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.
✓The receive optical power is too low, indicating a fiber or connector issue.Correct answer▾
Why this is correct
The receive power of -15.1 dBm is below the typical receive sensitivity for 10GBASE-SR (about -12.6 dBm). This causes bit errors that appear as CRC errors and runts. The transmit power is normal, so the issue is on the receive side, likely dirty connectors or a damaged fiber.
✗The SFP+ module is faulty and needs replacement.Wrong answer — click to see why▾
Why this is wrong here
The transceiver diagnostics show no fault flags, and the module is reporting nominal bit rate and other values within range.
✗The fiber patch cables are too long, exceeding the 300-meter distance limit for 10GBASE-SR over OM3 fiber.Wrong answer — click to see why▾
Why this is wrong here
The distance itself is within spec; the issue is the receive power being too low, not the distance exceeding the limit.
✗The interface speed is mismatched; the switch interface shows 1000Mb/s but the SFP+ is 10GBASE-SR.Wrong answer — click to see why▾
Why this is wrong here
This is a configuration mismatch, but it does not directly cause CRC errors. The CRC errors are due to low receive power.
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: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Trap categories for this question
Command / output trap
The exhibit shows the distance as 300 m, which is the maximum for 10GBASE-SR over OM3 fiber. While this is at the limit, the low receive power (-15.1 dBm) suggests excessive loss beyond the expected 2.6 dB over 300 m, indicating a problem with the fiber or connectors.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
- Static NAT maps one inside address to one outside address.
- PAT allows many inside hosts to share one public address using ports.
- Inside local and inside global describe the private and translated addresses.
- NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
- Identify inside and outside interfaces first.
- Check whether the scenario needs static NAT, dynamic NAT or PAT.
- Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Real-world example
How this comes up in practice
A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
What to study next
Got this wrong? Here's your next step.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related 200-301 NAT questions on configuration and troubleshooting.
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FAQ
Questions learners often ask
What does this 200-301 question test?
Static NAT maps one inside address to one outside address.
What is the correct answer to this question?
The correct answer is: The receive optical power is too low, indicating a fiber or connector issue. — The 'show interfaces' output shows 0 input errors and 0 CRC errors, but the symptom states high CRC errors—this indicates the exhibit is a red herring. However, the 'show interfaces transceiver details' reveals that the receive power is -15.1 dBm, which is below the typical receive sensitivity threshold for 10GBASE-SR (around -12.6 dBm). This low received optical power causes bit errors, which manifest as CRC errors and runts. The transmit power (-2.3 dBm) is normal, so the issue is likely a degraded fiber or dirty connector, not a faulty SFP.
What should I do if I get this 200-301 question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related 200-301 NAT questions on configuration and troubleshooting.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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