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350-501 MPLS and Segment Routing Practice Question

An SP network uses RSVP-TE for MPLS traffic engineering with FRR link protection. Which THREE statements are correct about RSVP-TE operation and FRR? (Choose three.)

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

In FRR link protection, the 1:1 detour method creates a separate backup LSP for each protected LSP, while the bypass tunnel method protects multiple LSPs over a single backup tunnel.

RSVP-TE uses PATH messages traveling downstream from headend to tailend and RESV messages traveling upstream from tailend to headend, establishing reservation state (D correct). The Explicit Route Object (ERO) in the PATH message specifies the strict or loose hops the traffic must traverse (E correct). For FRR link protection, the 1:1 detour method creates a separate backup LSP for each protected LSP, while the bypass tunnel method protects multiple LSPs over a single backup tunnel (B correct). Option A is incorrect because CSPF computes paths based on both IGP metrics and TE constraints (e.g., bandwidth, affinity), not only IGP metrics. Option C is incorrect because the 'fixed-filter' (FF) style is for per-sender reservation in RSVP, but MPLS-TE typically uses the 'shared-explicit' (SE) style to allow multiple senders (LSPs) to share the same reservation.

Answer analysis

Option-by-option breakdown

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

  • CSPF (Constrained Shortest Path First) is used to compute the best path based on IGP metrics only, ignoring TE constraints.

    Why it's wrong here

    Incorrect. CSPF considers TE constraints (bandwidth, affinity, explicit path).

  • In FRR link protection, the 1:1 detour method creates a separate backup LSP for each protected LSP, while the bypass tunnel method protects multiple LSPs over a single backup tunnel.

    Why this is correct

    Correct. 1:1 detour per LSP; bypass tunnel protects many.

  • The RSVP 'fixed-filter' (FF) reservation style is the only style used in MPLS-TE to allow multiple senders.

    Why it's wrong here

    Incorrect. 'shared-explicit' (SE) style is commonly used in MPLS-TE.

  • The PATH message travels from headend to tailend, while the RESV message travels from tailend back to headend, establishing reservation state.

    Why this is correct

    Correct. RSVP-TE uses PATH downstream and RESV upstream.

  • The Explicit Route Object (ERO) in the PATH message lists the strict or loose hops that the traffic must traverse.

    Why this is correct

    Correct. ERO specifies the explicit path.

Visual reference

Source Router + ACL permit 10.0.0.0/8 deny any Server 10.0.0.5 ✓ 192.168.1.1 ✗ dropped ACLs evaluate top-down; first match wins — implicit deny all at end

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Written by Johnson Ajibi, MSc IT Security

Senior Network & Security Engineer · founder of Courseiva

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