The answer is that transitive routing is not supported with VPC peering, so traffic cannot go through an intermediate VPC. Even when VPC A and VPC B are both directly peered with VPC C, there is no implicit path for packets to travel from A to B via C because each VPC peering connection is a strict one-to-one relationship. AWS route tables only forward traffic to the specific CIDR of the directly peered VPC, not to any networks reachable through that peer. On the AWS Certified SysOps Administrator Associate SOA-C02 exam, this concept frequently appears as a troubleshooting trap: you will see security groups and NACLs wide open, yet connectivity fails, and the hidden cause is an attempt to route through a third VPC. The exam tests your understanding that transitive routing is not supported with VPC peering, and the only solution is a direct peering connection between the two communicating VPCs. Remember the memory tip: “No hop, no hop—VPC peering is a one-hop stop.”
SOA-C02 Networking and Content Delivery Practice Question
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 troubleshooting connectivity issues between two VPCs that are peered together. The VPCs are in the same AWS region. An EC2 instance in VPC A (10.0.1.0/24) cannot ping an EC2 instance in VPC B (10.0.2.0/24). Both VPCs have route tables that include the CIDR of the other VPC with the peering connection as the target. The security groups and network ACLs allow all inbound and outbound traffic. What is the most likely issue?
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 the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
There is a third VPC C that is peered with both VPC A and VPC B, and VPC A is trying to reach VPC B through VPC C.
Option C is correct because transitive routing is not supported with VPC peering. Even though VPC A and VPC B are both peered with VPC C, traffic cannot flow from VPC A to VPC B through VPC C. Each VPC peering connection is a one-to-one relationship, and EC2 instances in VPC A cannot reach VPC B unless there is a direct VPC peering connection between them. The route tables in VPC A and VPC B must point directly to each other's CIDR via a direct peering connection, not through an intermediate VPC.
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 do not have a route to the other VPC's CIDR.
Why it's wrong here
The question states route tables include the CIDR.
✗
The VPC peering connection is not enabled for DNS resolution.
Why it's wrong here
DNS resolution is not required for basic ICMP connectivity.
✓
There is a third VPC C that is peered with both VPC A and VPC B, and VPC A is trying to reach VPC B through VPC C.
Why this is correct
VPC peering does not support transitive routing; traffic must go directly through the peering connection.
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.
✗
The VPCs are in different AWS regions.
Why it's wrong here
VPC peering works across regions, but the question states same region.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume VPC peering supports transitive routing, similar to a router in a traditional network, but AWS explicitly prohibits this — each peering connection is a direct, non-transitive link.
Detailed technical explanation
How to think about this question
VPC peering is a non-transitive, one-to-one networking connection. AWS explicitly does not support transitive peering, meaning if VPC A is peered with VPC C and VPC B is peered with VPC C, VPC A cannot route traffic to VPC B through VPC C. This is enforced at the AWS network layer; route tables in VPC A and VPC B would need a direct peering attachment to forward traffic between them. In contrast, AWS Transit Gateway does support transitive routing and can be used to connect multiple VPCs in a hub-and-spoke topology.
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.
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.
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: There is a third VPC C that is peered with both VPC A and VPC B, and VPC A is trying to reach VPC B through VPC C. — Option C is correct because transitive routing is not supported with VPC peering. Even though VPC A and VPC B are both peered with VPC C, traffic cannot flow from VPC A to VPC B through VPC C. Each VPC peering connection is a one-to-one relationship, and EC2 instances in VPC A cannot reach VPC B unless there is a direct VPC peering connection between them. The route tables in VPC A and VPC B must point directly to each other's CIDR via a direct peering connection, not through an intermediate VPC.
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.
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Question Discussion
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