- A
The VPC CIDR blocks overlap.
Why wrong: They are different: 10.0.0.0/16 and 10.1.0.0/16 do not overlap.
- B
The VPC peering connection is in a 'pending-acceptance' state.
Why wrong: If it were pending, the connection wouldn't be active; but once accepted, it's active.
- C
The route tables in each VPC do not have routes pointing to the peer VPC's CIDR.
Without routes, traffic will not be forwarded to the peering connection.
- D
The network ACLs in VPC A are blocking inbound traffic from VPC B's CIDR.
NACLs are stateless and must allow both inbound and outbound traffic.
- E
The security group rules in VPC A do not allow inbound traffic from VPC B's CIDR.
Security groups must allow traffic from the peer VPC.
Question 742 of 1,705
ANS-C01 Network Implementation Practice Question
This ANS-C01 practice question tests your understanding of network implementation. 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 company is troubleshooting connectivity issues between two VPCs that are peered using an inter-region VPC peering connection. The VPCs have the following CIDR blocks: VPC A (10.0.0.0/16) and VPC B (10.1.0.0/16). Which THREE of the following are possible reasons for the connectivity failure?
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 tables in each VPC do not have routes pointing to the peer VPC's CIDR.
Option C is correct because for inter-region VPC peering to function, each VPC must have explicit routes in its route tables pointing to the CIDR block of the peer VPC, with the VPC peering connection as the target. Without these routes, traffic destined for the peer VPC will not be forwarded over the peering link, causing connectivity failure.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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 VPC CIDR blocks overlap.
Why it's wrong here
They are different: 10.0.0.0/16 and 10.1.0.0/16 do not overlap.
- ✗
The VPC peering connection is in a 'pending-acceptance' state.
Why it's wrong here
If it were pending, the connection wouldn't be active; but once accepted, it's active.
- ✓
The route tables in each VPC do not have routes pointing to the peer VPC's CIDR.
Why this is correct
Without routes, traffic will not be forwarded to the peering connection.
Related concept
Read the scenario before looking for a memorised answer.
- ✓
The network ACLs in VPC A are blocking inbound traffic from VPC B's CIDR.
Why this is correct
NACLs are stateless and must allow both inbound and outbound traffic.
Related concept
Read the scenario before looking for a memorised answer.
- ✓
The security group rules in VPC A do not allow inbound traffic from VPC B's CIDR.
Why this is correct
Security groups must allow traffic from the peer VPC.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The ANS-C01 exam often tests the misconception that overlapping CIDRs are the only cause of peering failures, but here the CIDRs are non-overlapping, so candidates must recognize that missing routes and security group/NACL misconfigurations are equally valid causes.
Detailed technical explanation
How to think about this question
VPC peering relies on route table entries to direct traffic; without them, packets are dropped at the VPC boundary. Additionally, inter-region VPC peering supports transitive routing only if explicitly configured via route propagation or static routes, and security groups and network ACLs act as stateful and stateless firewalls respectively, which can block traffic even if routes are correct. In practice, a common troubleshooting step is to verify both route tables and security group/NACL rules simultaneously.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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.
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FAQ
Questions learners often ask
What does this ANS-C01 question test?
Network Implementation — This question tests Network Implementation — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The route tables in each VPC do not have routes pointing to the peer VPC's CIDR. — Option C is correct because for inter-region VPC peering to function, each VPC must have explicit routes in its route tables pointing to the CIDR block of the peer VPC, with the VPC peering connection as the target. Without these routes, traffic destined for the peer VPC will not be forwarded over the peering link, causing connectivity failure.
What should I do if I get this ANS-C01 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jul 4, 2026
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