- A
The route tables do not have a route to the other VPC's CIDR.
Why wrong: This is incorrect because the stem explicitly states that route tables in both VPCs include the CIDR of the other VPC with the peering connection as the target.
- B
The VPC peering connection is not enabled for DNS resolution.
This is correct. DNS resolution is required for hostname-based communication across peered VPCs. Without enabling it, ping by hostname will fail, while ping by IP would still work.
- C
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 wrong: This is not the most likely issue because the stem does not mention a third VPC. Transitive routing is not supported, but there is no evidence of a third VPC.
- D
The VPCs are in different AWS regions.
Why wrong: This is incorrect because the stem states the VPCs are in the same AWS region.
SOA-C02 VPC Peering DNS Resolution 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. A key principle to apply: vPC Peering DNS Resolution. 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 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 VPC peering connection is not enabled for DNS resolution.
Although the route tables and security groups/NACLs appear correctly configured, the scenario likely involves pinging by private DNS hostname rather than by IP address. For VPC peering, DNS resolution must be explicitly enabled on the peering connection to allow instances in one VPC to resolve the private DNS hostnames of instances in the peered VPC. Without this setting, a ping by hostname will fail even if ICMP traffic is allowed. The answer assumes the administrator is using private DNS hostnames for the ping.
Key principle: VPC Peering DNS Resolution
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
This is incorrect because the stem explicitly states that route tables in both VPCs include the CIDR of the other VPC with the peering connection as the target.
- ✓
The VPC peering connection is not enabled for DNS resolution.
Why this is correct
This is correct. DNS resolution is required for hostname-based communication across peered VPCs. Without enabling it, ping by hostname will fail, while ping by IP would still work.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
VPC Peering DNS Resolution
- ✗
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 it's wrong here
This is not the most likely issue because the stem does not mention a third VPC. Transitive routing is not supported, but there is no evidence of a third VPC.
- ✗
The VPCs are in different AWS regions.
Why it's wrong here
This is incorrect because the stem states the VPCs are in the same AWS region.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Candidates often forget that VPC peering does not automatically enable DNS resolution for hostnames. Here, the trap is that the question does not specify whether ping is by IP or hostname; the correct answer relies on the implicit use of hostnames. Without DNS resolution enabled, hostname-based pings fail even when routing and security rules are correct.
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
- VPC Peering DNS Resolution
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
VPC Peering DNS Resolution
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 vPC Peering DNS Resolution, then practise related SOA-C02 questions on the same topic to reinforce the concept.
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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 — VPC Peering DNS Resolution.
What is the correct answer to this question?
The correct answer is: The VPC peering connection is not enabled for DNS resolution. — Although the route tables and security groups/NACLs appear correctly configured, the scenario likely involves pinging by private DNS hostname rather than by IP address. For VPC peering, DNS resolution must be explicitly enabled on the peering connection to allow instances in one VPC to resolve the private DNS hostnames of instances in the peered VPC. Without this setting, a ping by hostname will fail even if ICMP traffic is allowed. The answer assumes the administrator is using private DNS hostnames for the ping.
What should I do if I get this SOA-C02 question wrong?
Review vPC Peering DNS Resolution, then practise related SOA-C02 questions on the same topic to reinforce the concept.
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?
VPC Peering DNS Resolution
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Last reviewed: Jun 24, 2026
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