The answer is a route-target mismatch on the new PEs, as this prevents the BGP autodiscovery process from importing remote VPLS endpoints into the local VFI. Even though the BGP session is established and L2VPN routes are exchanged, the pseudowire remains down because the receiving PE cannot associate those routes with the correct VPLS instance when the route-target does not match the existing VPLS context. This scenario is a classic trap on the Cisco SPCOR 350-501 exam, testing your understanding that BGP autodiscovery for VPLS relies entirely on route-target matching to build pseudowires—not just on BGP adjacency or route exchange. A common memory tip is “RT must match to stitch the VPLS patch”: if the route-targets don’t align, the pseudowire stays down even when everything else looks up.
350-501 Services Practice Question
This 350-501 practice question tests your understanding of services. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A service provider operates a Layer 2 MPLS VPN using VPLS. Recently, two new CE routers were added to the VPLS domain, but they cannot ping each other. The existing CEs can communicate. The network uses BGP autodiscovery and signaling. The new CEs are connected to different PEs. The 'show vfi status' command on the new PEs indicates the VFI is up but the pseudowire to the remote PE is down. The BGP session between the PEs is established and the L2VPN address family routes are exchanged. What is the most probable cause?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The route-target on the new PEs does not match the existing VPLS context
B is correct because BGP autodiscovery for VPLS relies on route-target (RT) matching to import remote VPLS endpoints into the local VFI. If the RT configured on the new PEs does not match the RT used by the existing VPLS context, the remote pseudowire will not be created even though BGP sessions are up and L2VPN routes are exchanged. The 'show vfi status' showing VFI up but pseudowire down is a classic symptom of RT mismatch, as the local PE cannot associate the received BGP routes with the correct VPLS instance.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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 BGP neighbor is not activated under the VPLS address-family
Why it's wrong here
Incorrect. If BGP L2VPN routes are exchanged, the neighbor is activated under the VPLS address-family.
✓
The route-target on the new PEs does not match the existing VPLS context
Why this is correct
Correct. Mismatched route-target prevents the new PEs from being discovered by the existing ones, so pseudowires are not established.
Related concept
Read the scenario before looking for a memorised answer.
✗
The MTU mismatch between PEs
Why it's wrong here
Incorrect. MTU mismatch would cause pseudowire status to show 'MTU mismatch' or similar, but the pseudowire may still be up.
✗
The VFI name is not consistent across PEs
Why it's wrong here
Incorrect. VFI names are locally significant; they do not need to match across PEs.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the distinction between BGP session establishment (which only requires neighbor configuration and address-family activation) and successful VPLS pseudowire creation (which additionally requires matching route-target import/export policies), leading candidates to incorrectly suspect BGP activation issues when the real problem is RT mismatch.
Trap categories for this question
Similar concept trap
Incorrect. MTU mismatch would cause pseudowire status to show 'MTU mismatch' or similar, but the pseudowire may still be up.
Command / output trap
Incorrect. MTU mismatch would cause pseudowire status to show 'MTU mismatch' or similar, but the pseudowire may still be up.
Detailed technical explanation
How to think about this question
In BGP autodiscovery for VPLS, each PE advertises a BGP L2VPN route containing a Route Distinguisher (RD) and a Route Target (RT) extended community. The receiving PE imports the route only if its local VPLS context has a matching RT import policy. The pseudowire is then signaled via LDP or BGP (depending on signaling method) using the VPLS ID from the BGP route. A common real-world pitfall is misconfiguring the RT on new PEs when scaling a VPLS domain, especially when using different RD/RT schemes across sites.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A network engineer at a university connects two campus buildings via a fibre link. Both routers run OSPF, but no adjacency forms — even though both routers can ping each other. The engineer finds one router is in area 0 and the other in area 1. OSPF adjacency requires matching area numbers, hello/dead timers, and network type. IP reachability alone is not enough.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Services — This question tests Services — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The route-target on the new PEs does not match the existing VPLS context — B is correct because BGP autodiscovery for VPLS relies on route-target (RT) matching to import remote VPLS endpoints into the local VFI. If the RT configured on the new PEs does not match the RT used by the existing VPLS context, the remote pseudowire will not be created even though BGP sessions are up and L2VPN routes are exchanged. The 'show vfi status' showing VFI up but pseudowire down is a classic symptom of RT mismatch, as the local PE cannot associate the received BGP routes with the correct VPLS instance.
What should I do if I get this 350-501 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
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.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.