hardMultiple Choice
300-410 Practice Question: A service provider network is experiencing MPLS…
A service provider network is experiencing MPLS label distribution failures between R1 and R2. R1 has: event manager applet LDP-MONITOR event syslog pattern "%LDP-4-ERROR" action 1.0 cli command "enable" action 2.0 cli command "clear mpls ldp neighbor *" action 3.0 syslog msg "Cleared LDP neighbors". Router R2 shows: LDP session is down, and logs show repeated LDP errors. What is the root cause?
⚠ Common exam trap
300-410 often tests EEM applet side effects — candidates focus on the LDP error itself and overlook that the applet's 'clear mpls ldp neighbor *' action is the actual cause of the persistent session down, mistaking the symptom for the root 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 EEM applet clears all LDP neighbors upon any LDP error, preventing the session from stabilizing.
The EEM applet is configured to trigger on the syslog pattern '%LDP-4-ERROR' and immediately execute 'clear mpls ldp neighbor *', which tears down all LDP sessions on R1. Each time LDP tries to re-establish and logs another error, the applet fires again, creating a loop that prevents the LDP session from ever stabilizing. The root cause is the overly aggressive automated remediation, not an LDP configuration issue on R2.
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 EEM applet clears all LDP neighbors upon any LDP error, preventing the session from stabilizing.
Why this is correct
The EEM applet triggers on any %LDP-4-ERROR syslog message and immediately clears all LDP neighbours. Each error therefore tears down the session before it can re-establish, creating the repeated failures and permanent down state on R2.
- ✗
The LDP router-id is misconfigured on R1.
Why it's wrong here
A mismatched LDP router-id prevents session establishment, but the stem shows repeated LDP errors and a down session rather than an ID conflict. It is tempting because router-id mismatch is a classic LDP fault, and it would be correct if the session failed immediately with ID mismatch messages.
- ✗
The syslog pattern matches only severity 4, but LDP errors are severity 3.
Why it's wrong here
The EEM applet's syslog pattern only triggers the remediation actions; it does not cause the LDP session to fail or produce the errors R2 reports. It is tempting because severity mismatches do stop applets firing, and it would be correct if the question asked why the automated clear command never ran.
- ✗
The MPLS label range is exhausted on R1.
Why it's wrong here
Label range exhaustion prevents new label bindings but does not tear down an established LDP session or generate repeated session-level errors. It is tempting because label exhaustion is a real MPLS fault, and it would be the answer if LDP sessions stayed up while specific prefixes failed to receive labels.
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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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Cisco exam blueprint
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