hardMultiple Choice
CCSP Practice Question: A multi-tier web application is deployed across…
A multi-tier web application is deployed across two VPCs connected via VPC peering. The web tier in VPC A must communicate with the database tier in VPC B on port 3306. Security groups are used for instance-level security. Which security group configuration is MOST secure?
⚠ Common exam trap
CCSP often tests the misconception that CIDR-based rules are equivalent to security group referencing, but the exam expects you to recognize that security group referencing is more secure and granular for instance-level access control.
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
✓
In the database security group, add an inbound rule allowing TCP/3306 from the security group ID of the web servers.
Referencing the web tier's security group ID as the source in the database security group's inbound rule creates a dynamic, identity-based trust relationship. Only instances that are members of that specific security group can initiate connections to port 3306, regardless of their IP addresses. This follows the principle of least privilege and is the most secure, maintainable approach in AWS VPC peering scenarios.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
In the database security group, add an inbound rule allowing TCP/3306 from the security group ID of the web servers.
Why this is correct
Referencing the web tier's security group ID as the source restricts inbound TCP/3306 to instances carrying that group, rather than opening the port to a CIDR range. This is the most secure option because membership is enforced at the instance level, even across peered VPCs.
- ✗
Configure a VPN connection between VPCs and use route tables to direct traffic.
Why it's wrong here
VPC peering already provides private connectivity between the two VPCs, so a VPN connection adds an unnecessary encrypted tunnel and route-table complexity without tightening the instance-level control the question asks about. A VPN would be right for connecting on-premises networks or VPCs that cannot be peered.
- ✗
In the network ACL for VPC B's subnet, add an inbound rule allowing TCP/3306 from VPC A CIDR.
Why it's wrong here
Network ACLs are stateless subnet-level filters, not instance-level security groups, so they cannot deliver the granular per-instance control the scenario specifies. They are tempting because they filter traffic at the subnet boundary, which suits broad deny rules, but security groups govern instance-level access here.
- ✗
In the database security group, add an inbound rule allowing TCP/3306 from the VPC A CIDR.
Why it's wrong here
A CIDR-based inbound rule permits every resource in VPC A to reach the database on 3306, not just the web tier, violating least privilege. It is tempting because it is simple and functional, but referencing the web tier's security group as the source restricts access to those specific instances.
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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official ISC2 exam blueprint
This CCSP practice question is part of Courseiva's free ISC2 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 CCSP exam.