PCNE Implementing Hybrid Interconnectivity Practice Question
An organization has established a Dedicated Interconnect to Google Cloud. They can ping instances in a VPC subnet but cannot connect to a service running on a different subnet within the same VPC. What is the most likely cause?
⚠ Common exam trap
Google Cloud often tests the misconception that firewall rules are the default cause of connectivity issues within a VPC, but here the key clue is that ping to one subnet works, isolating the problem to route advertisement rather than security policies.
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 BGP routes for that subnet are not advertised.
The Dedicated Interconnect is up and the organization can ping instances in one subnet, which confirms that Layer 2 and basic Layer 3 connectivity (via the VLAN attachment) are working. However, the inability to reach a service on a different subnet within the same VPC indicates that the on-premises router does not have a route to that specific subnet. This is most likely because the BGP session is not advertising the prefix for that subnet, or the on-premises router is not receiving the route via BGP. Without the route, traffic from on-premises to that subnet will be dropped.
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 MTU is too small.
Why it's wrong here
MTU issues typically cause packet loss or drops, not selective connectivity.
- ✗
The firewall rules are blocking the traffic.
Why it's wrong here
Firewall rules apply to all traffic regardless of the interconnect, so ping would also be blocked.
- ✗
The VLAN attachment is down.
Why it's wrong here
If the VLAN attachment were down, no traffic would flow at all.
- ✓
The BGP routes for that subnet are not advertised.
Why this is correct
If the on-premises router does not advertise the subnet via BGP, the VPC will not know how to route traffic back.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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.