The answer is that all IP addresses (0.0.0.0/0) are allowed to connect. This is because RDS security group rule evaluation with multiple groups attached follows a union model, where the effective inbound access is the combination of all rules across every attached group. Since sg-12345678 permits traffic from 0.0.0.0/0 on port 3306, that permissive rule applies regardless of the more restrictive rule in sg-87654321. On the AWS Certified Database Specialty DBS-C01 exam, this concept tests your understanding that security groups are additive and never override each other—a common trap is assuming the most restrictive rule wins, but the correct logic is that the most permissive rule governs. Remember the memory tip: "Security groups are like bouncers at a club—if one bouncer says everyone is allowed in, the whole club is open to all."
DBS-C01 Database Security Practice Question
This DBS-C01 practice question tests your understanding of database security. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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.
Network Topology
An RDS DB instance has two security groups attached. Security group sg-12345678 allows inbound traffic on port 3306 from 0.0.0.0/0. Security group sg-87654321 allows inbound traffic on port 3306 from 10.0.0.0/16. What is the effective inbound access to the DB instance?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
All IP addresses (0.0.0.0/0) are allowed to connect.
Option C is correct. Security group rules are evaluated together; the most permissive rule applies. Since sg-12345678 allows all IPs, the effective access is from 0.0.0.0/0. Option A is wrong because both groups apply. Option B is wrong because the more permissive rule dominates. Option D is wrong because there is no override of the more permissive rule.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
No IP addresses are allowed because the rules conflict.
Why it's wrong here
There is no conflict; rules are combined.
✗
Only the 0.0.0.0/0 range is allowed because sg-12345678 is more permissive.
Why it's wrong here
Both groups apply, so 10.0.0.0/16 is also allowed, but 0.0.0.0/0 includes all.
✗
Only the 10.0.0.0/16 range is allowed because sg-87654321 is more restrictive.
Why it's wrong here
Security group rules are additive; the broader allow from sg-12345678 also applies.
✓
All IP addresses (0.0.0.0/0) are allowed to connect.
Why this is correct
Since sg-12345678 allows all traffic, any IP can connect.
Related concept
Static NAT maps one inside address to one outside address.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
→Identify inside and outside interfaces first.
→Check whether the scenario needs static NAT, dynamic NAT or PAT.
→Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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 the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related DBS-C01 NAT questions on configuration and troubleshooting.
Database Security — This question tests Database Security — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: All IP addresses (0.0.0.0/0) are allowed to connect. — Option C is correct. Security group rules are evaluated together; the most permissive rule applies. Since sg-12345678 allows all IPs, the effective access is from 0.0.0.0/0. Option A is wrong because both groups apply. Option B is wrong because the more permissive rule dominates. Option D is wrong because there is no override of the more permissive rule.
What should I do if I get this DBS-C01 question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related DBS-C01 NAT questions on configuration and troubleshooting.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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Question Discussion
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