The answer is a CCM interval that is too short, causing false protection switchovers due to transient congestion. When MPLS-TP continuity check messages are sent too frequently, even minor, non-fatal network delays or buffer bloat can cause a few CCMs to be lost, which the working LSP’s RDI mechanism interprets as a signal failure, triggering an unnecessary 1:1 linear protection switch. On the Cisco SPCOR 350-501 exam, this scenario tests your understanding of the trade-off between detection speed and stability in MPLS-TP OAM; a common trap is to blame priority or OAM rate mismatches, but the root cause is simply an interval set too aggressively for the network’s jitter tolerance. Remember the memory tip: “Short CCM, false alarm—longer interval keeps the network calm.”
350-501 Architecture Practice Question
This 350-501 practice question tests your understanding of architecture. 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.
A service provider offers Carrier Ethernet services using MPLS-TP in the access and aggregation layers. The network uses MPLS-TP tunnels with static LSPs and protection via 1:1 linear protection with APS. One customer reports intermittent connectivity issues on their E-LINE service. The operations team observes that the protection switchover is occurring frequently due to apparent signal failures on the working path. However, the physical layer shows no errors. The protection switching is configured with revertive mode. The working LSP has an RDI (Remote Defect Indication) configured. Upon further investigation, the team finds that the working LSP's OAM continuity check messages (CCMs) are being lost occasionally, triggering a protection switch. What is the most likely misconfiguration?
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 the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The CCM interval is too short, causing frequent false failures due to transient congestion.
A short CCM interval makes the system sensitive to minor delays, causing false failures and frequent protection switches. A longer interval would reduce sensitivity but increase detection time. Priority and OAM rate differences are not typical causes.
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 CCM interval is too long, causing delayed detection.
Why it's wrong here
Incorrect. A too-long interval would cause slower detection, not frequent false switches.
✗
The working path uses a higher MPLS-TP OAM rate than the protection path.
Why it's wrong here
Incorrect. OAM rates are typically symmetrical and not a standard cause of false failures.
✗
The protection path has a lower priority than the working path.
Why it's wrong here
Incorrect. Priority settings do not cause false CCM loss.
✓
The CCM interval is too short, causing frequent false failures due to transient congestion.
Why this is correct
Correct. A short interval makes the system overly sensitive, leading to false failure detection.
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.
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 350-501 NAT questions on configuration and troubleshooting.
Architecture — This question tests Architecture — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: The CCM interval is too short, causing frequent false failures due to transient congestion. — A short CCM interval makes the system sensitive to minor delays, causing false failures and frequent protection switches. A longer interval would reduce sensitivity but increase detection time. Priority and OAM rate differences are not typical causes.
What should I do if I get this 350-501 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 350-501 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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