hardMultiple ChoiceObjective-mapped
300-410 Practice Question: An MPLS network uses LDP for label distribution
An MPLS network uses LDP for label distribution. After enabling Flexible NetFlow on the core routers, some LDP sessions fail to establish. Router R1 shows: show mpls ldp neighbor | include (Peer|State) Peer LDP Ident: 10.0.0.2:0, State: OPERATIONAL. Router R2 shows: show mpls ldp neighbor | include (Peer|State) Peer LDP Ident: 10.0.0.1:0, State: INIT. What is 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 flow monitor is using a sampler that samples only 1 out of 100 packets, causing LDP hello messages to be missed.
Flexible NetFlow can consume CPU resources or change the way packets are processed. In this case, the LDP session is stuck in INIT state, which typically indicates a problem with the transport connection or hello messages. If a flow monitor is applied to the interface used for LDP (e.g., the core-facing interface), it might be using a sampler that samples only a fraction of packets, causing LDP hello messages to be missed. Alternatively, the flow monitor might be configured to use a flow record that includes the 'ipv4 ttl' field, which could cause the router to process LDP packets differently. The correct answer is that a flow sampler is configured on the interface, causing LDP hello packets to be sampled and potentially dropped, preventing the LDP session from moving to OPERATIONAL.
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 flow monitor is using a sampler that samples only 1 out of 100 packets, causing LDP hello messages to be missed.
Why this is correct
LDP hellos are sent every 5 seconds; if they are sampled out, the neighbor will not receive them, and the session will stay in INIT.
- ✗
The LDP router-id is misconfigured, causing a conflict with the flow exporter.
Why it's wrong here
The LDP router-id is separate from flow exporter configuration.
- ✗
The MPLS MTU is set too low, causing LDP packets to be fragmented.
Why it's wrong here
Fragmentation would not cause INIT state; it would cause other issues.
- ✗
The flow exporter is configured to use TCP port 646, conflicting with LDP.
Why it's wrong here
LDP uses UDP and TCP port 646; the exporter uses UDP 2055 typically, so no conflict.
Go deeper
Related to this question
Learn chapter
Introduction to ENARSI Exam and Network Fundamentals
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.
Key term
NetFlow Configuration
NetFlow Configuration is the process of setting up Cisco devices to collect and export metadata about network traffic flows for monitoring, analysis, and troubleshooting.
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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.