350-501 Architecture Practice Question
A service provider is deploying Segment Routing (SR) with TI-LFA for fast convergence. Which mechanism does TI-LFA use to repair a link failure in a node segment path?
⚠ Common exam trap
Cisco often tests the misconception that TI-LFA is just an extension of classic LFA (Option B), but the key differentiator is that TI-LFA is topology-independent and uses a segment list, not a simple LFA next-hop.
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
✓
Precomputes a backup path using a segment list (label stack) that avoids the failed link
TI-LFA (Topology Independent Loop-Free Alternate) precomputes a backup path using a segment list (label stack) that explicitly avoids the failed link. This is achieved by encoding a repair path as a sequence of adjacency and node segments, ensuring that traffic is steered around the failure without loops, regardless of the network topology. The backup path is installed in the forwarding table before the failure occurs, enabling sub-50ms convergence.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Precomputes a backup path using a segment list (label stack) that avoids the failed link
Why this is correct
TI-LFA precomputes a backup path by inserting a segment list to steer traffic around the failure.
- ✗
Uses loop-free alternate (LFA) as defined in IPFRR
Why it's wrong here
LFA may not provide optimal coverage; TI-LFA extends LFA with segment routing.
- ✗
Uses RSVP-TE to signal a protected LSP
Why it's wrong here
RSVP-TE is not used in SR-TE; TI-LFA is independent of RSVP.
- ✗
Relies on BFD to trigger a backup path in the forwarding table
Why it's wrong here
BFD aids fast detection but does not compute the backup path.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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