- A
The IP SLA operation is not configured with a 'request-data-size' that matches the remote router's MTU, causing fragmentation and delay variations.
Why wrong: Incorrect because fragmentation would cause packet loss or increased delay, not negative values.
- B
The source and destination routers do not have synchronized clocks via NTP, causing one-way delay calculations to be inaccurate.
Correct. One-way delay is computed by subtracting the send timestamp from the receive timestamp. If clocks are not synchronized, the result can be negative or wildly inaccurate.
- C
The IP SLA operation is using a 'frequency' that is too high, causing the probes to overlap and corrupt the statistics.
Why wrong: Incorrect because overlapping probes would cause packet drops or retransmissions, not negative delay values.
- D
The remote router's IP SLA responder is not configured, so the source is using a different method to estimate delay.
Why wrong: Incorrect because without a responder, the UDP jitter operation would not work at all, not produce negative values.
Quick Answer
The answer is unsynchronized clocks between the source and destination routers, which is the most likely cause of negative one-way delay values in an IP SLA UDP jitter operation. One-way delay calculations rely on precise timestamping at both endpoints; without Network Time Protocol (NTP) synchronization, clock drift can cause the destination timestamp to appear earlier than the source timestamp, resulting in a negative computed delay. On the ENCOR 350-401 exam, this concept tests your understanding that IP SLA one-way delay metrics are meaningless without clock sync, and a common trap is assuming the issue lies with the UDP jitter configuration itself rather than the underlying time synchronization. Remember that IP SLA measures relative time, not absolute time—if the clocks disagree, the math breaks. A useful memory tip: "Negative delay means NTP is missing today."
CCNP IP SLA Practice Question
This 350-401 practice question tests your understanding of ip sla. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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.
An engineer configures IP SLA 30 to monitor the one-way delay to a remote site using UDP jitter. The operation is used to adjust routing metrics via route maps. The engineer notices that the IP SLA operation shows 'State: Active' but the one-way delay values are inconsistent, sometimes showing negative values. What is the most likely cause?
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 source and destination routers do not have synchronized clocks via NTP, causing one-way delay calculations to be inaccurate.
One-way delay measurements require clock synchronization between the source and destination routers. Without NTP, the clocks may drift, causing negative or inaccurate delay values.
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 IP SLA operation is not configured with a 'request-data-size' that matches the remote router's MTU, causing fragmentation and delay variations.
Why it's wrong here
Incorrect because fragmentation would cause packet loss or increased delay, not negative values.
- ✓
The source and destination routers do not have synchronized clocks via NTP, causing one-way delay calculations to be inaccurate.
Why this is correct
Correct. One-way delay is computed by subtracting the send timestamp from the receive timestamp. If clocks are not synchronized, the result can be negative or wildly inaccurate.
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.
- ✗
The IP SLA operation is using a 'frequency' that is too high, causing the probes to overlap and corrupt the statistics.
Why it's wrong here
Incorrect because overlapping probes would cause packet drops or retransmissions, not negative delay values.
- ✗
The remote router's IP SLA responder is not configured, so the source is using a different method to estimate delay.
Why it's wrong here
Incorrect because without a responder, the UDP jitter operation would not work at all, not produce negative values.
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.
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 350-401 NAT questions on configuration and troubleshooting.
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FAQ
Questions learners often ask
What does this 350-401 question test?
IP SLA — This question tests IP SLA — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: The source and destination routers do not have synchronized clocks via NTP, causing one-way delay calculations to be inaccurate. — One-way delay measurements require clock synchronization between the source and destination routers. Without NTP, the clocks may drift, causing negative or inaccurate delay values.
What should I do if I get this 350-401 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 350-401 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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Last reviewed: Jun 18, 2026
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