mediumMultiple ChoiceObjective-mapped
300-410 Practice Question: Is troubleshooting MPLS traffic where packets are…
A network engineer is troubleshooting MPLS traffic where packets are being dropped at a P router. The engineer runs show mpls forwarding-table and sees that the outgoing label for a specific FEC is 'Untagged' instead of a valid label. The IGP is running correctly, and LDP neighbors are 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
✓
LDP is not enabled on the outgoing interface.
The 'Untagged' label in the LFIB indicates that LDP has not assigned a label for that FEC on the outgoing interface. This typically happens when LDP is not enabled on the outgoing interface, either because the interface is not configured with mpls ip or because the interface is passive under LDP.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
LDP is not enabled on the outgoing interface.
Why this is correct
Correct because LDP must be enabled on each interface to assign a label for the FEC; without it, the label remains 'Untagged' and packets are dropped.
- ✗
The IGP metric is too high, causing LDP to prefer a different path.
Why it's wrong here
Incorrect because LDP uses IGP next-hop; if the IGP metric is high, LDP still assigns a label, but the path may be suboptimal.
- ✗
The mpls label range is exhausted.
Why it's wrong here
Incorrect because label exhaustion would cause LDP to fail to allocate labels, but the symptom would be 'No label' or 'Label allocation failed', not 'Untagged'.
- ✗
The router is configured with mpls ldp advertise-labels for host routes only.
Why it's wrong here
Incorrect because this command controls which prefixes are advertised, not whether LDP is enabled on an interface; the FEC would not be advertised at all, not show as 'Untagged'.
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.
About these practice questions
This 300-410 question is part of Courseiva's 1,966-question bank — original exam-style content with full explanations and wrong-answer analysis, never real exam questions or exam 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 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.