350-501 MPLS and Segment Routing Practice Question
A network architect is designing an MPLS network that must provide fast convergence in case of a link failure. The network uses Segment Routing. Which mechanism provides sub-50ms protection by using a precomputed backup path?
⚠ Common exam trap
Cisco often tests the distinction between failure detection (BFD) and failure repair (FRR mechanisms), and the trap here is that candidates confuse BFD's fast detection with the actual precomputed backup path provided by TI-LFA.
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
✓
TI-LFA (Topology-Independent Loop-Free Alternate)
B is correct because TI-LFA (Topology-Independent Loop-Free Alternate) is a Segment Routing mechanism that precomputes a backup path using a segment list, enabling sub-50ms convergence upon link failure. It guarantees loop-free forwarding even in complex topologies where traditional LFA may fail, by leveraging SR's source routing capabilities.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
BFD (Bidirectional Forwarding Detection)
Why it's wrong here
BFD detects failures but does not provide a backup path.
- ✓
TI-LFA (Topology-Independent Loop-Free Alternate)
Why this is correct
TI-LFA uses segment lists to guarantee backup path regardless of topology.
- ✗
LFA (Loop-Free Alternate)
Why it's wrong here
LFA may not provide protection for all topologies.
- ✗
LDP FRR
Why it's wrong here
LDP FRR uses LFA, not TI-LFA, and does not provide topology-independence.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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