The answer is to verify that the DB subnet group includes a public subnet with an internet gateway. This is correct because even when a database is marked as publicly accessible, the underlying DB subnet group must contain at least one subnet that is routed to an internet gateway; without that route, the public IP address assigned to the RDS instance cannot be reached from outside the VPC. On the AWS Certified Database Specialty DBS-C01 exam, this question tests your understanding of how network connectivity layers interact—specifically, that security group rules alone are insufficient if the subnet’s route table lacks an internet gateway. A common trap is assuming “publicly accessible” automatically grants external access, but the subnet group configuration is the gatekeeper. Memory tip: “Public subnet + IGW = public access; private subnet = no public access, regardless of the checkbox.”
DBS-C01 Monitoring and Troubleshooting Practice Question
This DBS-C01 practice question tests your understanding of monitoring and troubleshooting. 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 developer reports that an application is unable to connect to an Amazon RDS for Oracle database. The security group for the database allows inbound traffic on port 1521 from the application's security group. The database is publicly accessible. What should be checked next?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Verify that the DB subnet group includes a public subnet with an internet gateway.
Option A is correct because even if the security group allows traffic, the DB subnet group must be in a public subnet with an internet gateway. Option B is wrong because the issue is connectivity, not backups. Option C is wrong because CloudWatch Logs may not show connection attempts. Option D is wrong because parameter groups don't control network access.
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.
✗
Check the DB parameter group for the 'remote_listener' parameter.
Why it's wrong here
Parameter group changes don't affect network connectivity.
✗
Check the automated backup retention period.
Why it's wrong here
Backup retention does not affect connectivity.
✓
Verify that the DB subnet group includes a public subnet with an internet gateway.
Why this is correct
Public accessibility requires a public subnet and internet gateway.
Error logs may not show failed connection attempts.
Common exam traps
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.
Trap categories for this question
Command / output trap
Error logs may not show failed connection attempts.
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 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.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related DBS-C01 subnetting questions on CIDR, address ranges, and subnet selection.
Monitoring and Troubleshooting — This question tests Monitoring and Troubleshooting — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: Verify that the DB subnet group includes a public subnet with an internet gateway. — Option A is correct because even if the security group allows traffic, the DB subnet group must be in a public subnet with an internet gateway. Option B is wrong because the issue is connectivity, not backups. Option C is wrong because CloudWatch Logs may not show connection attempts. Option D is wrong because parameter groups don't control network access.
What should I do if I get this DBS-C01 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 DBS-C01 subnetting questions on CIDR, address ranges, and subnet selection.
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 →
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 developer reports that an application is unable to connect to an Amazon RDS for MySQL DB instance. The security group for the DB instance allows inbound traffic on port 3306 from the application server's security group. The DB instance is in a VPC with both public and private subnets. The application server is in a private subnet. What is the most likely cause of the connection failure?
easy
A.The DB instance is in a public subnet and the application server is in a private subnet, so they cannot communicate.
✓ B.The security group for the DB instance does not allow inbound traffic from the application server's security group.
C.The network ACL for the private subnet is blocking outbound traffic to the DB instance.
D.The DB instance is not part of a DB subnet group that includes the private subnet.
Why B: If the DB instance is in a public subnet and the application server is in a private subnet, they are in different subnets within the same VPC, so they can communicate via private IPs if routing is correct. However, the most common issue is that the security group rule is not correctly associated or the DB instance is in a public subnet with a public DNS name that resolves to a public IP, but the private subnet cannot reach the internet. But the question implies the DB instance is in a public subnet; private subnet instances can reach public subnet instances via the VPC router. However, often the misconfiguration is that the DB instance's security group does not allow traffic from the application server's security group. Option D is correct because the security group rule might be missing or incorrect. Option A is wrong because NACLs are stateless and typically allow all outbound. Option B is wrong because the DB instance is in a public subnet, but the application server is in a private subnet, they can communicate within the VPC. Option C is wrong because the DB subnet group is for Multi-AZ, not single instance.
Last reviewed: Jun 20, 2026
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This DBS-C01 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 DBS-C01 exam.
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