ANS-C01 Network Design Practice Question
A company has a VPC with a CIDR block of 10.0.0.0/16. They have two subnets: subnet-A (10.0.1.0/24) and subnet-B (10.0.2.0/24). An EC2 instance in subnet-A needs to communicate with an RDS database in subnet-B. Both subnets are in the same Availability Zone. What is the most efficient way to enable this communication?
⚠ Common exam trap
The trap here is that candidates may overthink the scenario and assume that different subnets require additional networking components like a Transit Gateway or VPC Peering, forgetting that subnets within the same VPC inherently have local connectivity via the VPC's route table.
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
✓
No additional configuration is required. The instance and database can communicate within the same VPC.
Both the EC2 instance and the RDS database reside within the same VPC (10.0.0.0/16), and subnets within a VPC can communicate with each other by default using the VPC's local route. No additional configuration is needed, as the VPC's main route table or subnet route tables already include a local route for the VPC CIDR, enabling direct communication within the same Availability Zone.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Create a Transit Gateway and attach both subnets to it.
Why it's wrong here
Transit Gateway is for connecting multiple VPCs or on-premises, not needed within a single VPC.
- ✗
Place a NAT Gateway in subnet-A and configure route tables accordingly.
Why it's wrong here
NAT Gateway is for internet access, not internal VPC communication.
- ✓
No additional configuration is required. The instance and database can communicate within the same VPC.
Why this is correct
VPC internal routing allows communication between subnets in the same VPC.
- ✗
Create a VPC Peering connection between the two subnets.
Why it's wrong here
VPC Peering is for connecting different VPCs, not subnets within the same VPC.
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Same concept, more angles
1 more way this is tested on ANS-C01
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 company has a VPC with a CIDR block of 192.168.0.0/16. They have two subnets: Subnet A (192.168.1.0/24) and Subnet B (192.168.2.0/24). They launch an EC2 instance in Subnet A and another EC2 instance in Subnet B. They want to ensure that both instances can communicate with each other. The instances are in the same VPC. What is the simplest way to enable communication between these instances?
easy- A.Create a VPC Peering connection between Subnet A and Subnet B
- ✓ B.No additional configuration is needed; instances in the same VPC can communicate by default
- C.Create a NAT Gateway in each subnet
- D.Attach an internet gateway to the VPC
Why B: By default, all instances within the same VPC can communicate with each other using private IP addresses, regardless of which subnet they reside in. The VPC's implicit router enables this layer-3 connectivity as long as the subnets' route tables do not explicitly block traffic and the instances' security groups or network ACLs permit the traffic. Since both subnets are within the same VPC (192.168.0.0/16), no additional configuration is required for basic IP-level communication.
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This ANS-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 ANS-C01 exam.