- A
The Cloud Router is configured to only accept routes from a specific set of prefixes
Cloud Router can be configured with custom route advertisements or filters that limit which prefixes are accepted from a BGP peer.
- B
The VPC firewall rules are blocking BGP traffic (TCP port 179)
Why wrong: BGP sessions are established, so firewall is not blocking BGP traffic.
- C
The Cloud Router is configured with a higher MED value for the route
Why wrong: MED affects route preference, not route acceptance.
- D
The on-premises router is not sending the AS_PATH attribute
Why wrong: AS_PATH is mandatory in BGP updates; missing it would break the session.
Question 807 of 982
PCNE Practice Question: Designing, Planning, and Prototyping a GCP Network
This PCNE practice question tests your understanding of designing, planning, and prototyping a gcp network. 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 network engineer is troubleshooting BGP route propagation between an on-premises network and a GCP VPC via Cloud Router. The on-premises router is advertising a specific subnet (10.1.0.0/16), but GCP is not receiving the route. Cloud Router BGP sessions are established. Which configuration could be the issue?
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 Cloud Router is configured to only accept routes from a specific set of prefixes
Cloud Router has an option to set custom route advertisements. If the on-premises route is not being accepted, it could be because the Cloud Router is configured with 'advertised route priority' or 'advertised IP ranges' that exclude the on-premises prefixes. More likely, the BGP peer is configured to accept only specific prefixes via 'advertised route priority' or 'advertised groups'. Another common issue: the on-premises router needs to advertise the route; Cloud Router must have 'advertise custom routes' enabled or the route must be within the allowed prefixes.
Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
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 Cloud Router is configured to only accept routes from a specific set of prefixes
- ✗
The VPC firewall rules are blocking BGP traffic (TCP port 179)
- ✗
The Cloud Router is configured with a higher MED value for the route
Why it's wrong here
MED affects route preference, not route acceptance.
- ✗
The on-premises router is not sending the AS_PATH attribute
Why it's wrong here
AS_PATH is mandatory in BGP updates; missing it would break the session.
Common exam traps
Common exam trap: usable hosts are not the same as total addresses
Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.
Detailed technical explanation
How to think about this question
Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.
KKey Concepts to Remember
- CIDR notation defines the prefix length.
- Block size helps identify subnet boundaries.
- Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
- The required host count determines the smallest suitable subnet.
TExam Day Tips
- Write the block size before choosing the subnet.
- Check whether the question asks for hosts, subnets or a specific address range.
- Do not confuse /24, /25, /26 and /27 host counts.
Key takeaway
Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
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.
Visual reference
What to study next
Got this wrong? Here's your next step.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related PCNE subnetting questions on CIDR, address ranges, and subnet selection.
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Designing, Planning, and Prototyping a GCP Network — study guide chapter
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FAQ
Questions learners often ask
What does this PCNE question test?
Designing, Planning, and Prototyping a GCP Network — This question tests Designing, Planning, and Prototyping a GCP Network — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: The Cloud Router is configured to only accept routes from a specific set of prefixes — Cloud Router has an option to set custom route advertisements. If the on-premises route is not being accepted, it could be because the Cloud Router is configured with 'advertised route priority' or 'advertised IP ranges' that exclude the on-premises prefixes. More likely, the BGP peer is configured to accept only specific prefixes via 'advertised route priority' or 'advertised groups'. Another common issue: the on-premises router needs to advertise the route; Cloud Router must have 'advertise custom routes' enabled or the route must be within the allowed prefixes.
What should I do if I get this PCNE question wrong?
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related PCNE subnetting questions on CIDR, address ranges, and subnet selection.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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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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