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MPLS and Segment RoutinghardMultiple ChoiceObjective-mapped

350-501 MPLS and Segment Routing Practice Question

An MPLS network is experiencing micro-loops during convergence after a link failure. The network uses LDP and IS-IS as IGP. Which of the following solutions can prevent micro-loops during IGP convergence without requiring additional protocols?

⚠ Common exam trap

Cisco often tests the distinction between IGP-integrated solutions (LFA) and overlay protocols (RSVP-TE, BGP), so the trap here is assuming that any fast-reroute mechanism requires an additional protocol like RSVP-TE, when LFA is a native IGP feature.

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

Configure LFA (Loop-Free Alternate) on the IGP.

LFA (Loop-Free Alternate) is a feature built directly into IGPs like IS-IS and OSPF that precomputes a backup next-hop that does not loop back to the failed link. This prevents micro-loops during IGP convergence without requiring any additional protocols such as RSVP-TE or BGP, making it a lightweight, protocol-integrated solution.

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

  • Implement MPLS-TE FRR using bypass tunnels.

    Why it's wrong here

    TE FRR is for RSVP-TE tunnels, not for native LDP/IGP.

  • Enable BGP PIC (Prefix Independent Convergence).

    Why it's wrong here

    BGP PIC handles BGP routes, not IGP micro-loops.

  • Configure LFA (Loop-Free Alternate) on the IGP.

    Why this is correct

    LFA computes backup paths that avoid loops during convergence.

  • Deploy RSVP-TE with fast-reroute.

    Why it's wrong here

    RSVP-TE is a separate protocol, not needed for IGP micro-loop avoidance.

Visual reference

R1 R2 R3 R4 10 100 10 100 OSPF picks R1→R2→R4 (cost 20) over R1→R3→R4 (cost 200)

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Written by Johnson Ajibi, MSc IT Security

Senior Network & Security Engineer · founder of Courseiva

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