hardMultiple Choice
350-401 Practice Question: Is configuring MPLS TE (Traffic Engineering) in…
A network engineer is configuring MPLS TE (Traffic Engineering) in an MPLS core to optimize bandwidth utilization. After enabling MPLS TE on all core routers and configuring tunnels, the engineer notices that traffic is not being rerouted when a link fails. The 'show mpls traffic-eng tunnels' shows the tunnels are up but not using the backup path. What is the most likely missing configuration?
⚠ Common exam trap
Cisco often tests the distinction between MPLS TE tunnel establishment and MPLS TE protection mechanisms; candidates mistakenly assume that simply enabling MPLS TE and configuring tunnels automatically provides fast reroute, but FRR is a separate configuration step requiring explicit backup tunnel definitions.
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
✓
MPLS TE FRR (Fast Reroute) is not configured on the tunnels.
MPLS TE Fast Reroute (FRR) is the mechanism that provides local protection and rapid traffic rerouting upon link or node failure. Without FRR configured on the tunnels, the head-end router must detect the failure, recompute the path, and signal a new LSP, which is a slow process. The fact that tunnels are up but not using a backup path indicates that FRR backup tunnels (e.g., link or node protection) have not been configured, so traffic continues to flow through the failed link until the head-end reacts.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
MPLS TE FRR (Fast Reroute) is not configured on the tunnels.
Why this is correct
MPLS TE Fast Reroute is the mechanism that provisions pre-established bypass tunnels to protect specific links or nodes along the primary TE path. Without FRR, a link failure forces the headend LSR to detect the outage, recompute a new path using CSPF, and re-signal the tunnel, resulting in a multi-second outage. Enabling FRR with the 'fast-reroute' or 'link protection' keyword under the tunnel interface is what actually installs precomputed backup paths for immediate local protection.
- ✗
LDP is not enabled on the core interfaces.
Why it's wrong here
LDP is a label distribution protocol that operates independently from MPLS TE, which relies on RSVP-TE for tunnel signaling. Even if LDP is fully enabled on all core interfaces, it only provides best-effort label switching and cannot create protected TE tunnels. The absence of LDP would not cause the lack of backup paths; that is the role of TE FRR.
- ✗
RSVP is not configured on the core routers.
Why it's wrong here
RSVP is indeed required for MPLS TE signaling, as it reserves bandwidth and establishes the TE tunnel path, but it does not automatically provide protection. The configuration of RSVP-TE alone does not create bypass tunnels; without explicit FRR and link protection under the tunnel configuration, a failure on the primary path would require headend rerouting. Thus, while RSVP is necessary, its presence alone does not yield backup paths.
- ✗
OSPF is not configured with MPLS TE extensions.
Why it's wrong here
OSPF TE extensions are required for building a traffic engineering database that lets CSPF compute an optimal path for the TE tunnel, but they contribute nothing to protecting that path. Flooding extended link attributes like bandwidth and delay does not trigger any backup path creation or auto-protection. Therefore, even with OSPF TE fully operational, the tunnel would still lack FRR protection unless explicitly configured.
Go deeper
Related to this question
About these practice questions
Courseiva writes every 350-401 question from scratch — 1,923 in total, each with an explanation and a wrong-answer breakdown. None are copied from real exams or dumps. Learn why practice questions differ from exam dumps →
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 350-401 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 350-401 exam.