The answer is that VPC A must have a custom route with a destination inside VPC B and a next-hop set to the appliance, and that custom route must be exported to VPC B via the VPC peering connection. This works because Google Cloud’s VPC peering does not automatically share custom routes; you must explicitly export them from the originating VPC, and the route itself must point to an internal next-hop appliance (like a firewall or NAT instance) within VPC A to intercept and process traffic destined for VPC B. On the Google Professional Cloud Network Engineer exam, this scenario tests your understanding of route exchange mechanics and the distinction between dynamic and custom static routes—a common trap is assuming the appliance can be in a different region or that firewall rules alone satisfy the routing condition. Remember the two-part rule: the route must exist in the source VPC, and it must be exported over the peering. Memory tip: “Export the custom, point to the box.”
PCNE Implementing a Virtual Private Cloud Practice Question
This PCNE practice question tests your understanding of implementing a virtual private cloud. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 company has VPC peering between two VPC networks. They want to ensure that traffic from VPC A to VPC B can use a custom route in VPC A that points to a next-hop appliance in VPC A. Which TWO conditions must be met?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
VPC peering must be set up with 'export custom routes' enabled from VPC A.
Option B is required because custom routes must be exported via peering to be used by the peer network. Option C is required because a route in VPC A with destination in VPC B and next-hop appliance is needed. Option A is not required; the appliance can be in any region. Option D is not required for the forward path, though return path needs separate configuration. Option E is a general firewall requirement but not specific to the custom route usage.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
VPC B must have a route back to VPC A.
Why it's wrong here
Return path is not required for the forward path condition.
✓
VPC peering must be set up with 'export custom routes' enabled from VPC A.
Why this is correct
Export of custom routes is required for the peer to see and use them.
Related concept
Static NAT maps one inside address to one outside address.
✗
The appliance must be in the same region as VPC A.
Why it's wrong here
The appliance can be in any region within VPC A; region does not affect route usage.
✗
The appliance must have a firewall rule allowing traffic from VPC B.
Why it's wrong here
Firewall rules are needed but not specific to the custom route export condition.
✓
VPC A must have a route with destination inside VPC B and next-hop set to the appliance.
Why this is correct
This is the custom route directing traffic to the appliance.
Related concept
Static NAT maps one inside address to one outside address.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
→Identify inside and outside interfaces first.
→Check whether the scenario needs static NAT, dynamic NAT or PAT.
→Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Real-world example
How this comes up in practice
A healthcare organisation deploys an application with a public-facing web tier and a private database tier. The database subnet has no public IP and only accepts connections from the web tier's security group. Questions like this test whether you can design cloud network isolation using VNets/VPCs, subnets, and security group rules.
What to study next
Got this wrong? Here's your next step.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related PCNE NAT questions on configuration and troubleshooting.
Implementing a Virtual Private Cloud — This question tests Implementing a Virtual Private Cloud — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: VPC peering must be set up with 'export custom routes' enabled from VPC A. — Option B is required because custom routes must be exported via peering to be used by the peer network. Option C is required because a route in VPC A with destination in VPC B and next-hop appliance is needed. Option A is not required; the appliance can be in any region. Option D is not required for the forward path, though return path needs separate configuration. Option E is a general firewall requirement but not specific to the custom route usage.
What should I do if I get this PCNE question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related PCNE NAT questions on configuration and troubleshooting.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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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.
Question Discussion
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