- A
The route tables in both VPCs do not have routes to the peer VPC CIDR.
Without routes pointing to the peering connection, traffic cannot be forwarded between VPCs.
- B
VPC peering does not support cross-account connections.
Why wrong: VPC peering supports cross-account connections across different accounts.
- C
The CIDR blocks overlap, causing routing conflicts.
Why wrong: The problem states non-overlapping CIDR blocks, so this is not the issue.
- D
The security groups in VPC-B do not allow inbound ICMP traffic from VPC-A.
Why wrong: While this could be an issue, the most likely first cause is missing routes; security groups are stateful but need rules for inbound.
Question 1,481 of 1,546
Troubleshooting VPC Peering: Routes Not Added to Route Tables
This SOA-C02 practice question tests your understanding of networking and content delivery. 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 SysOps Administrator is setting up a VPC peering connection between two VPCs (VPC-A and VPC-B) in different AWS accounts. After the peering connection is accepted, instances in VPC-A cannot ping instances in VPC-B. Both VPCs have non-overlapping CIDR blocks. What is the MOST likely cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"most likely"Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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 both VPCs do not have routes to the peer VPC CIDR.
The most likely cause is that the route tables in both VPCs do not have routes to the peer VPC CIDR. Even after a VPC peering connection is accepted, traffic cannot flow between the VPCs unless explicit routes are added to each VPC's route table pointing to the CIDR block of the peer VPC, with the VPC peering connection as the target. Without these routes, instances in VPC-A have no path to reach instances in VPC-B, so ping fails.
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 tables in both VPCs do not have routes to the peer VPC CIDR.
Why this is correct
Without routes pointing to the peering connection, traffic cannot be forwarded between VPCs.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
VPC peering does not support cross-account connections.
Why it's wrong here
VPC peering supports cross-account connections across different accounts.
- ✗
The CIDR blocks overlap, causing routing conflicts.
Why it's wrong here
The problem states non-overlapping CIDR blocks, so this is not the issue.
- ✗
The security groups in VPC-B do not allow inbound ICMP traffic from VPC-A.
Why it's wrong here
While this could be an issue, the most likely first cause is missing routes; security groups are stateful but need rules for inbound.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume security groups or NACLs are the primary cause of connectivity issues, but the foundational routing layer must be correctly configured first for any traffic to flow across a VPC peering connection.
Detailed technical explanation
How to think about this question
VPC peering is a one-to-one networking connection that does not support transitive routing; each VPC must have its own route table entries for the peer CIDR. Additionally, security groups and network ACLs are stateful or stateless filters that apply after routing decisions, so if routes are missing, packets are dropped at the routing layer before any security rules are checked. In a cross-account scenario, the owner of each VPC must separately add these routes, and the peering connection must be in the 'active' state.
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.
Visual reference
What to study next
Got this wrong? Here's your next step.
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FAQ
Questions learners often ask
What does this SOA-C02 question test?
Networking and Content Delivery — This question tests Networking and Content Delivery — 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 both VPCs do not have routes to the peer VPC CIDR. — The most likely cause is that the route tables in both VPCs do not have routes to the peer VPC CIDR. Even after a VPC peering connection is accepted, traffic cannot flow between the VPCs unless explicit routes are added to each VPC's route table pointing to the CIDR block of the peer VPC, with the VPC peering connection as the target. Without these routes, instances in VPC-A have no path to reach instances in VPC-B, so ping fails.
What should I do if I get this SOA-C02 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Same concept, more angles
2 more ways this is tested on SOA-C02
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A SysOps administrator is troubleshooting connectivity between two VPCs (VPC-A and VPC-B) connected via a VPC Peering connection. An EC2 instance in VPC-A cannot ping an EC2 instance in VPC-B. The route tables and security groups are correctly configured. Which THREE steps should the administrator take to resolve the issue?
hard- A.Add a route in VPC-A's subnet route table pointing to the VPC Peering connection for VPC-B's CIDR
- B.Configure VPC Peering as a transit gateway
- ✓ C.Verify that VPC-B does not have a VPN connection to an on-premises network
- ✓ D.Ensure the VPC Peering connection is in the 'active' state
- ✓ E.Check the Network ACLs in both VPCs to ensure inbound/outbound ICMP traffic is allowed
Why C: The correct steps are C, D, and E. Option C: If VPC-B has a VPN connection to an on-premises network, traffic from VPC-A to VPC-B could be routed asymmetrically or via the VPN, disrupting the VPC peering connectivity. Verifying that VPC-B does not have such a VPN connection ensures traffic intended for VPC-B stays within the peering connection. Option D: The VPC peering connection must be in the 'active' state for traffic to flow. If it is pending acceptance or rejected, no traffic can pass. The administrator should verify the state and accept the request if necessary. Option E: Network ACLs are stateless and can block ICMP traffic. Even if security groups allow ICMP, NACLs must allow both inbound and outbound ICMP (echo request and reply) for ping to work. Option A is incorrect because the route tables are already correctly configured (as stated in the problem), so adding another route is unnecessary and could cause issues. Option B is incorrect because a VPC peering connection is not a transit gateway; it is a direct one-to-one connection and does not support transitive routing.
Variation 2. A SysOps administrator is troubleshooting connectivity issues between two VPCs in different AWS Regions. Both VPCs are connected via a VPC Peering connection. The route tables in both VPCs have routes pointing to the peering connection. Security groups allow all traffic. However, an EC2 instance in VPC A cannot ping an EC2 instance in VPC B. What is the most likely cause?
hard- A.The network ACLs in subnets are blocking ICMP traffic.
- B.VPC Peering is not supported across AWS Regions.
- ✓ C.The route tables in the subnets where the instances reside do not include a route to the peered VPC's CIDR.
- D.The security groups do not allow traffic from the peered VPC's security group ID.
Why C: The most likely cause is that the route tables associated with the subnets where the EC2 instances reside do not include a route to the peered VPC's CIDR block. Even if the main VPC route tables have the peering route, each subnet must be explicitly associated with a route table that contains the route to the peered VPC's CIDR; otherwise, traffic from the instance will not be directed to the VPC peering connection.
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Last reviewed: Jun 24, 2026
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