mediumMultiple ChoiceObjective-mapped
300-410 Practice Question: Is troubleshooting an MPLS L2VPN (VPWS) where the…
A network engineer is troubleshooting an MPLS L2VPN (VPWS) where the pseudowire between two PE routers is down. The show mpls l2transport vc command displays state 'down' and the VC ID is correct on both ends. The engineer checks the MPLS LDP session and sees it is up, but the targeted LDP session for the pseudowire is not established. What is the most likely cause?
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
✓
The mpls ldp neighbor command is missing on one or both PEs.
For a pseudowire to be established, a targeted LDP session is required between the two PE routers. If the targeted LDP session is not established, the pseudowire cannot exchange labels. The most common cause is that the mpls ldp neighbor command is missing or misconfigured on one or both PEs.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
The mpls ldp neighbor command is missing on one or both PEs.
Why this is correct
Correct because targeted LDP sessions require explicit configuration using the mpls ldp neighbor command to initiate the session for pseudowire signaling.
- ✗
The VC ID does not match on both ends.
Why it's wrong here
Incorrect because the stem states the VC ID is correct on both ends; a mismatch would cause a different symptom.
- ✗
The IGP is not converging, causing reachability issues.
Why it's wrong here
Incorrect because the LDP session is up, indicating IGP reachability is fine; the targeted session is a separate issue.
- ✗
The mpls label protocol ldp command is missing globally.
Why it's wrong here
Incorrect because LDP is already operational (session up), so the global protocol is configured; the targeted session requires additional configuration.
Go deeper
Related to this question
Learn chapter
Introduction to ENARSI Exam and Network Fundamentals
Key term
MPLS Label Distribution
MPLS Label Distribution is the process by which routers exchange labels that tell them how to forward packets across a network without looking at the IP address each time.
Key term
LDP Protocol
LDP, or Label Distribution Protocol, is a protocol that routers use to automatically exchange labels that enable MPLS (Multiprotocol Label Switching) to create fast, efficient paths for data packets across a network.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 300-410 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 300-410 exam.