This ANS-C01 practice question tests your understanding of network design. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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.
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?
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.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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.
Related concept
Read the scenario before looking for a memorised answer.
✗
Create a NAT Gateway in each subnet
Why it's wrong here
NATGateway is for internet access, not internal communication.
Common exam trap: answer the scenario, not the keyword
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.
Detailed technical explanation
How to think about this question
The VPC's implicit router uses the main route table (or custom route tables) to direct traffic between subnets based on the VPC CIDR. Each subnet's route table automatically includes a local route for the VPC CIDR (e.g., 192.168.0.0/16), which ensures that traffic destined for any IP within the VPC is forwarded locally without needing a gateway or peering. Security groups and network ACLs must still allow the traffic, but by default, security groups allow all outbound traffic and network ACLs allow all inbound/outbound traffic, so no changes are needed for basic ICMP or TCP/UDP communication.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A healthcare organisation deploys an application with a public-facing web tier and a private database tier. The database subnet has no public IP and only accepts connections from the web tier's security group. Questions like this test whether you can design cloud network isolation using VNets/VPCs, subnets, and security group rules.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Network Design — This question tests Network Design — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: 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.
What should I do if I get this ANS-C01 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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