ANS-C01 Network Design Practice Question
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?
⚠ Common exam trap
The trap here is that candidates may overthink the scenario and assume that different subnets require explicit routing or peering, when in fact the VPC's implicit local route already handles all intra-VPC traffic by default.
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 needed; instances in the same VPC can communicate by default
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.
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 VPC Peering connection between Subnet A and Subnet B
Why it's wrong here
VPC Peering is for different VPCs.
- ✓
No additional configuration is needed; instances in the same VPC can communicate by default
Why this is correct
Default VPC routing allows communication between subnets.
- ✗
Create a NAT Gateway in each subnet
Why it's wrong here
NAT Gateway is for internet access, not internal communication.
- ✗
Attach an internet gateway to the VPC
Why it's wrong here
Internet gateway is for internet access.
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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.