350-501 Services Practice Question
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?
⚠ Common exam trap
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.
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 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.
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.
- ✗
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.
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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.