350-501 Architecture Practice Question
An engineer notices that an MPLS LSP in the core is not establishing. Which troubleshooting step should be performed first?
⚠ Common exam trap
Cisco often tests the misconception that checking IGP adjacency (OSPF) is the first step, but LDP depends on IGP for reachability, not adjacency; the trap is that candidates confuse routing protocol adjacency with label distribution protocol adjacency.
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
✓
Verify LDP neighbor adjacency
The first step in troubleshooting an MPLS LSP that is not establishing is to verify LDP neighbor adjacency because LDP is the protocol responsible for distributing labels across the MPLS domain. Without a working LDP session between adjacent LSRs, label bindings cannot be exchanged, and the LSP cannot be built. This is the foundational layer for MPLS forwarding, so it must be checked before higher-layer issues like routing or reachability.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Verify LDP neighbor adjacency
Why this is correct
LDP adjacency is essential for label exchange and LSP building.
- ✗
Ping the far-end loopback interface
Why it's wrong here
Ping tests reachability, not LSP.
- ✗
Check BGP IPv4 unicast neighbors
Why it's wrong here
BGP is not required for LSP establishment.
- ✗
Check OSPF neighbor adjacency on all links
Why it's wrong here
OSPF may not be used for MPLS.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 350-501 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 350-501 exam.