The answer is to check VPC Flow Logs and review security group rules. VPC Flow Logs capture IP traffic metadata for network interfaces, allowing you to analyze traffic patterns and identify packet drops, latency spikes, or asymmetric routing between the EC2 instance and RDS database. Security group rules must be verified because they act as a virtual firewall at the instance level; if outbound rules on the EC2 side or inbound rules on the RDS side are misconfigured, they can silently drop or throttle traffic, causing slow connections even when the database is reachable. On the AWS Certified Advanced Networking Specialty ANS-C01 exam, this scenario tests your understanding of stateful versus stateless filtering and the diagnostic hierarchy—many candidates mistakenly jump to NACLs or route tables, but since both resources are in the same VPC, NACLs are stateless and can block return traffic, while the default route only affects internet-bound traffic. A quick memory tip: for same-VPC slowness, think “Flow Logs first, then Security Groups—NACLs are a trap, routes are for the map.”
ANS-C01 Network Security, Compliance and Governance Practice Question
This ANS-C01 practice question tests your understanding of network security, compliance and governance. 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 network engineer is troubleshooting connectivity issues between an EC2 instance and an RDS database in the same VPC. The EC2 instance can connect to the database, but the connection is slow. Which TWO actions should the engineer take to diagnose the issue? (Choose TWO.)
Verify the route table for the database subnet to ensure there is a default route to the internet.
Why wrong: Not relevant for internal traffic.
B
Check the network ACL for the database subnet to ensure it is stateful.
Why wrong: NACLs are stateless; they need explicit rules for return traffic.
C
Verify that the security group for the EC2 instance allows outbound traffic on the database port, and the database security group allows inbound from the EC2 instance.
Security group misconfigurations can cause slow connections.
D
Check VPC Flow Logs to analyze traffic patterns and identify drops or latency.
Flow Logs provide visibility into traffic.
E
Check the route propagation settings on the VPC.
Why wrong: Not relevant for intra-VPC connectivity.
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 security group for the EC2 instance allows outbound traffic on the database port, and the database security group allows inbound from the EC2 instance.
Options A and B are correct. Checking security group rules (A) ensures proper allow rules. Reviewing VPC Flow Logs (B) can reveal dropped packets or latency. Option C is wrong because NACLs are stateless and may drop return traffic. Option D is wrong because the default route is not relevant to internal traffic. Option E is wrong because route propagation is for VPN/Direct Connect.
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.
✗
Verify the route table for the database subnet to ensure there is a default route to the internet.
Why it's wrong here
Not relevant for internal traffic.
✗
Check the network ACL for the database subnet to ensure it is stateful.
Why it's wrong here
NACLs are stateless; they need explicit rules for return traffic.
✓
Verify that the security group for the EC2 instance allows outbound traffic on the database port, and the database security group allows inbound from the EC2 instance.
Why this is correct
Security group misconfigurations can cause slow connections.
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 ANS-C01 subnetting questions on CIDR, address ranges, and subnet selection.
Network Security, Compliance and Governance — This question tests Network Security, Compliance and Governance — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: Verify that the security group for the EC2 instance allows outbound traffic on the database port, and the database security group allows inbound from the EC2 instance. — Options A and B are correct. Checking security group rules (A) ensures proper allow rules. Reviewing VPC Flow Logs (B) can reveal dropped packets or latency. Option C is wrong because NACLs are stateless and may drop return traffic. Option D is wrong because the default route is not relevant to internal traffic. Option E is wrong because route propagation is for VPN/Direct Connect.
What should I do if I get this ANS-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 ANS-C01 subnetting questions on CIDR, address ranges, and subnet selection.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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