- A
Incorrect VLAN ID on the VLAN attachment
Why wrong: VLAN ID mismatch would prevent the tunnel from establishing, not cause BGP flapping.
- B
Mismatched BGP hold timer values
If the hold timers differ, the session may time out and flap.
- C
MTU mismatch causing packet fragmentation
MTU issues can cause BGP packets to be dropped, leading to session flapping.
- D
Incorrect BGP password (MD5 authentication)
MD5 password mismatch causes BGP session to fail and flap.
- E
Duplicate AS number on the on-premises router
Why wrong: Duplicate AS numbers would cause BGP to reject updates, not flap.
Question 988 of 1,000
PCNE Implementing Hybrid Interconnectivity Practice Question
This PCNE practice question tests your understanding of implementing hybrid interconnectivity. 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.
An engineer is troubleshooting a High Availability VPN setup. The VPN tunnels are established, but the BGP sessions are flapping. Which THREE factors could cause this? (Choose THREE.)
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
✓
Mismatched BGP hold timer values
BGP session flapping can be caused by mismatched parameters, MTU issues, or authentication problems.
Key principle: A trunk being up does not mean the VLAN is allowed across it. Always verify the allowed VLAN list and whether the VLAN exists on both switches.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Incorrect VLAN ID on the VLAN attachment
- ✓
Mismatched BGP hold timer values
Why this is correct
If the hold timers differ, the session may time out and flap.
Related concept
Access ports place end devices into a single VLAN.
- ✓
MTU mismatch causing packet fragmentation
- ✓
Incorrect BGP password (MD5 authentication)
- ✗
Duplicate AS number on the on-premises router
Why it's wrong here
Duplicate AS numbers would cause BGP to reject updates, not flap.
Common exam traps
Common exam trap: an active trunk can still block the VLAN you need
A trunk being up does not prove every VLAN is crossing it. Check allowed VLAN lists, native VLAN mismatch, VLAN existence and access-port assignment.
Detailed technical explanation
How to think about this question
VLAN questions usually combine access-port and trunking clues. The key is to identify whether the issue is local to one switchport, caused by the trunk, or caused by the VLAN not existing where it needs to exist.
KKey Concepts to Remember
- Access ports place end devices into a single VLAN.
- Trunk ports carry multiple VLANs between switches.
- Allowed VLAN lists decide which VLANs can cross a trunk.
- Native VLAN mismatch can create confusing symptoms.
TExam Day Tips
- Use show vlan brief to verify access VLANs.
- Use show interfaces trunk to verify trunk state and allowed VLANs.
- Do not treat every same-VLAN issue as a routing problem.
Key takeaway
A trunk being up does not mean the VLAN is allowed across it. Always verify the allowed VLAN list and whether the VLAN exists on both switches.
Real-world example
How this comes up in practice
A company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
What to study next
Got this wrong? Here's your next step.
Review VLAN allowed lists, native VLAN mismatch detection, and how to verify VLAN membership with show vlan brief and show interfaces trunk. Then practise related PCNE questions on switching, trunking, and access-port configuration.
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Implementing Hybrid Interconnectivity — study guide chapter
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FAQ
Questions learners often ask
What does this PCNE question test?
Implementing Hybrid Interconnectivity — This question tests Implementing Hybrid Interconnectivity — Access ports place end devices into a single VLAN..
What is the correct answer to this question?
The correct answer is: Mismatched BGP hold timer values — BGP session flapping can be caused by mismatched parameters, MTU issues, or authentication problems.
What should I do if I get this PCNE question wrong?
Review VLAN allowed lists, native VLAN mismatch detection, and how to verify VLAN membership with show vlan brief and show interfaces trunk. Then practise related PCNE questions on switching, trunking, and access-port configuration.
What is the key concept behind this question?
Access ports place end devices into a single VLAN.
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Last reviewed: Jul 4, 2026
This PCNE practice question is part of Courseiva's free Google Cloud 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 PCNE exam.
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