350-501 Services Practice Question
In a Segment Routing network with TI-LFA enabled, which mechanism prevents micro-loops during a link failure?
⚠ Common exam trap
Cisco often tests the distinction between TI-LFA and traditional LFA, where candidates mistakenly think LFA alone prevents micro-loops, but TI-LFA specifically adds segment lists and delay timers to address this issue.
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
✓
Explicit path with segment list and delay timer
In Segment Routing with TI-LFA, micro-loops are prevented by using an explicit path with a segment list and a delay timer. When a link fails, the protecting router installs a backup path with a segment list that steers traffic around the failure, and a delay timer ensures that the backup path is not activated until the network has converged, preventing transient loops.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Constraint Shortest Path First computation
Why it's wrong here
Incorrect. CSPF is used for path computation in MPLS-TE, not for loop avoidance.
- ✓
Explicit path with segment list and delay timer
Why this is correct
Correct. TI-LFA encodes a post-convergence path as an explicit segment list and introduces a delay to allow other routers to converge, preventing micro-loops.
- ✗
Loop-Free Alternate precomputed backup paths
Why it's wrong here
Incorrect. LFA provides protection but may create micro-loops in certain failure scenarios.
- ✗
Prefix Independent Convergence with fast reroute
Why it's wrong here
Incorrect. PIC provides fast convergence but does not inherently prevent micro-loops.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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