Question 1hardmultiple choice
Full question →hardmultiple choiceObjective-mapped
A network engineer is troubleshooting intermittent packet loss on a 10 km single-mode fiber link between two buildings. The link lights are on, but the interface shows a high number of CRC errors. The engineer has cleaned the fiber connectors and replaced the patch cables. What should the engineer check NEXT?
Answer choices
Why each option matters
Good practice is not just finding the correct option. The wrong answers often show the exact trap the exam wants you to fall into.
A
Best answer
Check the transmit/receive optical power levels
Insufficient optical power (signal too weak) can cause CRC errors. Checking power levels verifies the link budget is adequate.
B
Distractor review
Check the duplex settings on both ends
Fiber optic links typically operate at full duplex; duplex mismatch is rare and would cause late collisions, not CRC errors.
C
Distractor review
Verify the cable length is within specifications
Single-mode fiber can support distances well beyond 10 km; length is unlikely to be the issue if it was previously working.
D
Distractor review
Adjust the Spanning Tree Protocol priority
STP priority affects path selection, not physical layer errors like CRC.
Common exam trap
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.
Technical deep dive
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.
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More questions from this exam
Keep practising from the same exam bank, or move into a focused topic page if this question exposed a weak area.
Question 1
A network engineer needs to connect two switches located 400 meters apart. The cable run includes high electromagnetic interference from nearby machinery. The engineer decides to use fiber optic cabling. Which transceiver type and fiber combination should be used to ensure the link reaches 400 meters while remaining cost-effective?
Question 2
A network engineer is designing a new switched network and needs to ensure that broadcast traffic from one department does not reach another department's workstations. The engineer plans to use VLANs. Which of the following must be configured on the switches to isolate broadcast domains as intended?
Question 3
A security engineer is configuring a site-to-site VPN between two branch offices. The requirement is to encrypt all traffic between the two networks using IPsec. Which IPsec mode should be used to encrypt the entire IP packet including the original header?
Question 4
A network administrator is connecting two switches to increase bandwidth and provide redundancy. Which technology should be used to combine multiple physical links into a single logical link?
Question 5
A network administrator is experiencing issues where unauthorized devices are offering IP addresses to clients, causing connectivity problems. Which security feature should be enabled on switches to prevent this?
Question 6
A network administrator is troubleshooting a connectivity issue and suspects the problem is related to the physical cabling. At which layer of the OSI model should the administrator begin their investigation?
FAQ
Questions learners often ask
What does this N10-009 question test?
Static NAT maps one inside address to one outside address.
What is the correct answer to this question?
The correct answer is: Check the transmit/receive optical power levels — CRC errors on a fiber link often indicate signal integrity issues. After cleaning connectors and replacing patch cables, the next step is to check the optical power levels (transmit and receive) to ensure they are within the acceptable range for the GBICs/SFPs. A weak signal due to attenuation (e.g., from long distance or dirty connectors) can cause errors. Duplex settings are not typically an issue on fiber links as they are usually fixed. Cable length is within the 10 km limit for single-mode fiber. STP priority does not cause CRC errors.
What should I do if I get this N10-009 question wrong?
Then try more questions from the same exam bank and focus on understanding why the wrong options are tempting.
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