The answer is that the VPC Peering connection does not have 'Enable DNS Resolution' enabled. When instances in VPC A can ping the private IP of instances in VPC B but not their DNS names, the issue is almost always that DNS resolution across the peering link is disabled by default. Even with correct route tables and working ICMP traffic, AWS does not automatically forward DNS queries between peered VPCs; you must explicitly enable the 'Enable DNS Resolution' option on the peering connection, which also requires the 'Enable DNS Hostnames' setting to be turned on in both VPCs. On the AWS Certified SysOps Administrator Associate SOA-C02 exam, this is a classic trap: many candidates assume that if ping works, DNS must work too, but the exam tests your understanding that VPC Peering separates the network layer from the DNS layer. A common memory tip is "Ping is layer 3, DNS is layer 7—peering only bridges the network, not the resolver."
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 using a VPC Peering connection. The instances in VPC A can ping the private IP of instances in VPC B, but not the DNS names. 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 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 does not have 'Enable DNS Resolution' enabled.
VPC Peering does not support DNS resolution across VPCs by default unless the 'Enable DNS Resolution' option is enabled in the peering connection. Option A is irrelevant because route tables are correct (ping works). Option B is incorrect because DNS hostnames are separate from resolution. Option D is incorrect because security groups affect traffic, not DNS resolution.
Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
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 VPC A do not have a route to VPC B's CIDR.
Why it's wrong here
Ping works, so routing is correct.
✗
The security groups in VPC B block DNS traffic (port 53).
Why it's wrong here
DNS resolution is a VPC feature, not instance-level.
✓
The VPC Peering connection does not have 'Enable DNS Resolution' enabled.
Why this is correct
DNS resolution across VPC peering requires this option.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Common exam trap: usable hosts are not the same as total addresses
Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.
Detailed technical explanation
How to think about this question
Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.
KKey Concepts to Remember
CIDR notation defines the prefix length.
Block size helps identify subnet boundaries.
Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
The required host count determines the smallest suitable subnet.
TExam Day Tips
→Write the block size before choosing the subnet.
→Check whether the question asks for hosts, subnets or a specific address range.
→Do not confuse /24, /25, /26 and /27 host counts.
Key takeaway
Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
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.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related SOA-C02 subnetting questions on CIDR, address ranges, and subnet selection.
Networking and Content Delivery — This question tests Networking and Content Delivery — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: The VPC Peering connection does not have 'Enable DNS Resolution' enabled. — VPC Peering does not support DNS resolution across VPCs by default unless the 'Enable DNS Resolution' option is enabled in the peering connection. Option A is irrelevant because route tables are correct (ping works). Option B is incorrect because DNS hostnames are separate from resolution. Option D is incorrect because security groups affect traffic, not DNS resolution.
What should I do if I get this SOA-C02 question wrong?
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related SOA-C02 subnetting questions on CIDR, address ranges, and subnet selection.
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?
CIDR notation defines the prefix length.
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 →
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
This SOA-C02 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the SOA-C02 exam.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.