The answer is that the VPC peering connection is not in the 'active' state. Even if a route table correctly lists the peered VPC’s CIDR (10.1.0.0/16) pointing to the peering connection, traffic will fail if the peering itself is in a non-active state like pending-acceptance, expired, or failed—effectively creating a black hole route. This scenario tests your understanding that a VPC peering route is only functional when the connection status is 'active', a critical distinction when troubleshooting VPC peering connectivity issues. On the AWS Certified Advanced Networking Specialty ANS-C01 exam, this concept often appears in scenario-based questions where a route table looks correct but connectivity fails, trapping candidates who overlook the peering state. Remember the mnemonic: "Active is the only path—any other state is a black hole."
ANS-C01 Network Design Practice Question
This ANS-C01 practice question tests your understanding of network design. 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.
Network Topology
A network engineer is troubleshooting connectivity between a VPC (10.0.0.0/16) and a peered VPC (10.1.0.0/16). The route table shown is associated with subnet-aaa. An EC2 instance in subnet-aaa cannot reach an instance in the peered VPC. What is the issue?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The VPC peering connection is not in the 'active' state
Option D is correct because a VPC peering connection must be in the 'active' state for traffic to flow between the VPCs. If the peering connection is in any other state (e.g., 'pending-acceptance', 'expired', 'failed', or 'deleted'), the route to the peered VPC's CIDR will be considered a black hole, and the EC2 instance in subnet-aaa will be unable to reach the instance in the peered VPC. The route table shown includes a route for 10.1.0.0/16 pointing to the peering connection, but the connection's state must be verified as 'active' for the route to be effective.
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 route to the peered VPC's CIDR is missing
Why it's wrong here
The route to 10.1.0.0/16 via the peering connection is present.
✗
The route table does not have a route to an Internet Gateway
Why it's wrong here
Internet access is not required for VPC peering communication; the route to NATgateway is for internet, not peering.
✗
The route table is not associated with the correct subnet
Why it's wrong here
The exhibit shows an association with subnet-aaa, so it is associated.
✓
The VPC peering connection is not in the 'active' state
Why this is correct
If the peering connection is pending or rejected, traffic will not flow even though the route exists.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
AWS often tests the misconception that simply adding a route to the peered VPC's CIDR in the route table is sufficient for connectivity, but the trap here is that the VPC peering connection must be in the 'active' state; otherwise, the route is a black hole and traffic will not flow.
Trap categories for this question
Command / output trap
The exhibit shows an association with subnet-aaa, so it is associated.
Detailed technical explanation
How to think about this question
VPC peering connections are established as a one-to-one relationship between two VPCs and must be explicitly accepted by the accepter VPC owner to transition from 'pending-acceptance' to 'active'. Even after activation, route tables in both VPCs must have routes pointing to the peering connection ID for the respective CIDRs, and security groups or network ACLs must permit the traffic. A common subtlety is that a peering connection can become 'expired' if not accepted within 7 days, or 'failed' if the VPCs have overlapping CIDRs, which would render the route ineffective despite its presence.
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 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.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Network Design — This question tests Network Design — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The VPC peering connection is not in the 'active' state — Option D is correct because a VPC peering connection must be in the 'active' state for traffic to flow between the VPCs. If the peering connection is in any other state (e.g., 'pending-acceptance', 'expired', 'failed', or 'deleted'), the route to the peered VPC's CIDR will be considered a black hole, and the EC2 instance in subnet-aaa will be unable to reach the instance in the peered VPC. The route table shown includes a route for 10.1.0.0/16 pointing to the peering connection, but the connection's state must be verified as 'active' for the route to be effective.
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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Question Discussion
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