The answer is that no additional configuration is required, as same VPC subnet communication is enabled by default. This is because the VPC’s internal router inherently allows traffic between all subnets within its CIDR block, provided that the associated security groups and network ACLs permit the flow. On the AWS Certified Advanced Networking Specialty ANS-C01 exam, this concept tests your understanding of VPC fundamentals versus more complex networking constructs; a common trap is overthinking the scenario and reaching for VPC Peering or a Transit Gateway, which are only needed for cross-VPC or hybrid connectivity. Remember that within a single VPC, subnets communicate natively without any gateways or peering—the default route table already handles local routing. A useful memory tip: “Same VPC, same local route—no extra gear needed for the route.”
ANS-C01 Network Design Practice Question
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 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?
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.
Option A is correct. By default, VPC subnets can communicate with each other; no additional configuration is needed if the security groups and network ACLs allow traffic. Option B is wrong because VPC Peering is for cross-VPC communication. Option C is wrong because a NATGateway is for outbound internet access. Option D is wrong because a Transit Gateway is for connecting multiple VPCs or networks.
Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
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
NATGateway 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.
Common exam traps
Common exam trap: usable hosts are not the same as total addresses
Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.
Detailed technical explanation
How to think about this question
Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.
KKey Concepts to Remember
CIDR notation defines the prefix length.
Block size helps identify subnet boundaries.
Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
The required host count determines the smallest suitable subnet.
TExam Day Tips
→Write the block size before choosing the subnet.
→Check whether the question asks for hosts, subnets or a specific address range.
→Do not confuse /24, /25, /26 and /27 host counts.
Key takeaway
Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Real-world example
How this comes up in practice
A company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
What to study next
Got this wrong? Here's your next step.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related ANS-C01 subnetting questions on CIDR, address ranges, and subnet selection.
Network Design — This question tests Network Design — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: No additional configuration is required. The instance and database can communicate within the same VPC. — Option A is correct. By default, VPC subnets can communicate with each other; no additional configuration is needed if the security groups and network ACLs allow traffic. Option B is wrong because VPC Peering is for cross-VPC communication. Option C is wrong because a NAT Gateway is for outbound internet access. Option D is wrong because a Transit Gateway is for connecting multiple VPCs or networks.
What should I do if I get this ANS-C01 question wrong?
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related ANS-C01 subnetting questions on CIDR, address ranges, and subnet selection.
What is the key concept behind this question?
CIDR notation defines the prefix length.
About these practice questions
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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.
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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.
Question Discussion
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