Question 876 of 1,663
DBS-C01 Security Group Evaluation Practice Question
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?
⚠ Common exam trap
Candidates often mistakenly think that security groups apply only the most restrictive rule, or that rules conflict. In reality, rules are additive and the most permissive rule takes effect.
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
✓
All IP addresses (0.0.0.0/0) are allowed to connect.
When multiple security groups are attached to an RDS instance, the rules are combined, and the most permissive inbound rule applies. Security group sg-12345678 allows all IP addresses (0.0.0.0/0), so the effective inbound access is from all IPs. Option A is wrong because the rules do not conflict; they are additive. Option B is wrong because the more restrictive rule does not override the more permissive one. Option C is wrong because the less restrictive rule (0.0.0.0/0) applies, not just the 10.0.0.0/16 range.
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.
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 →
Last reviewed: Jun 20, 2026
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.
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.