350-501 Architecture Practice Question
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?
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 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.
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.
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Written by Johnson Ajibi, MSc IT Security
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