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Networking and Content Delivery →hardMultiple ChoiceObjective-mapped

Quick Answer

The answer is to first check the route table for the private subnet, ensuring it has a 0.0.0.0/0 route pointing to the NAT Gateway. This is the most common failure point when troubleshooting NAT Gateway internet access from a private subnet, because without that default route, traffic from private instances has no path to the NAT Gateway and cannot reach external services like 203.0.113.50:443. On the AWS Certified SysOps Administrator Associate SOA-C02 exam, this scenario tests your understanding of VPC routing fundamentals—many candidates mistakenly check security groups or the NAT Gateway’s public IP first, but those are secondary; the route table is the immediate suspect. A common trap is forgetting that NACLs and security groups are stateful for NAT traffic, so they rarely cause outbound-only failures. Memory tip: “Route before rules”—always verify the private subnet’s route table before diving into firewall configurations.

SOA-C02 Networking and Content Delivery Practice Question

This SOA-C02 practice question tests your understanding of networking and content delivery. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 public and private subnets. A NAT Gateway is deployed in the public subnet to allow instances in the private subnet to access the internet. However, private instances cannot reach an external service at 203.0.113.50:443. What should be checked first?

Clue words in this question

Noticing these words before you look at the options changes how you read each choice.

  • Clue: "first"

    Why it matters: Order matters here. You are being tested on which action comes before the others — not which action is generally useful.

Question 1hardmultiple choice
Read the full NAT/PAT explanation →

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

✓

The route table for the private subnet has a route 0.0.0.0/0 pointing to the NAT Gateway.

Option B is correct because the most common issue is that the route table for the private subnet does not have a default route pointing to the NAT Gateway. Option A is wrong because NACLs and security groups are stateful for NAT Gateway traffic, but the route table is the first thing to verify. Option C is wrong because the NAT Gateway's public IP is not relevant; the issue is routing. Option D is wrong because the internet gateway is needed for the NAT Gateway, but if private instances cannot reach the external service, the routing from the private subnet to the NAT Gateway is the primary suspect.

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.

  • ✓

    The route table for the private subnet has a route 0.0.0.0/0 pointing to the NAT Gateway.

    Why this is correct

    Without this route, traffic from private instances cannot reach the NAT Gateway, so they cannot access the internet.

    Clue confirmation

    The clue word "first" in the question point toward this answer.

    Related concept

    CIDR notation defines the prefix length.

  • ✗

    The NAT Gateway has an Elastic IP assigned.

    Why it's wrong here

    The NAT Gateway must have an EIP, but that is typically configured at creation. Lack of EIP would prevent outbound traffic, but routing is checked first.

  • ✗

    The security group for the NAT Gateway allows inbound traffic from the private subnet.

    Why it's wrong here

    NAT Gateway security groups are not configurable; it uses security groups only for the ENI, but the default allows all traffic. NACLs may block, but routing is more likely.

  • ✗

    The internet gateway is attached to the VPC.

    Why it's wrong here

    If the NAT Gateway itself can't reach the internet, the IGW might be missing, but the immediate issue is routing from private subnet to NAT Gateway.

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 SOA-C02 subnetting questions on CIDR, address ranges, and subnet selection.

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FAQ

Questions learners often ask

What does this SOA-C02 question test?

Networking and Content Delivery — This question tests Networking and Content Delivery — CIDR notation defines the prefix length..

What is the correct answer to this question?

The correct answer is: The route table for the private subnet has a route 0.0.0.0/0 pointing to the NAT Gateway. — Option B is correct because the most common issue is that the route table for the private subnet does not have a default route pointing to the NAT Gateway. Option A is wrong because NACLs and security groups are stateful for NAT Gateway traffic, but the route table is the first thing to verify. Option C is wrong because the NAT Gateway's public IP is not relevant; the issue is routing. Option D is wrong because the internet gateway is needed for the NAT Gateway, but if private instances cannot reach the external service, the routing from the private subnet to the NAT Gateway is the primary suspect.

What should I do if I get this SOA-C02 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 SOA-C02 subnetting questions on CIDR, address ranges, and subnet selection.

Are there clue words in this question I should notice?

Yes — watch for: "first". Order matters here. You are being tested on which action comes before the others — not which action is generally useful.

What is the key concept behind this question?

CIDR notation defines the prefix length.

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Same concept, more angles

2 more ways this is tested on SOA-C02

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 public and private subnets. A NAT Gateway is deployed in the public subnet. Private EC2 instances need to download patches from the internet. The route table for the private subnet has a default route (0.0.0.0/0) pointing to the NAT Gateway. However, the instances cannot reach the internet. What is the most likely cause?

hard
  • A.The private subnet’s network ACL is blocking outbound traffic.
  • ✓ B.The NAT Gateway is not placed in a public subnet with a route to an internet gateway.
  • C.The security group for the private instances does not allow outbound HTTPS.
  • D.The NAT Gateway does not have an Elastic IP address assigned.

Why B: Option C is correct because the NAT Gateway must be in a public subnet with an internet gateway route. If the NAT Gateway's subnet's route table does not have a default route to an internet gateway, the NAT Gateway cannot forward traffic to the internet. Option A is wrong because the NAT Gateway does not need a public IP for outbound-only traffic (though it helps). Option B is irrelevant to internet access. Option D is wrong because security groups for private instances should allow outbound traffic.

Variation 2. A company has a VPC with public and private subnets. A NAT Gateway is in the public subnet, and a private EC2 instance needs to download patches from the internet. The instance can reach the internet after a reboot. Which action should the SysOps administrator take to make the internet access persistent?

hard
  • ✓ A.Update the route table of the private subnet to point 0.0.0.0/0 to the NAT Gateway.
  • B.Attach an internet gateway to the private subnet.
  • C.Associate an Elastic IP with the NAT Gateway.
  • D.Enable DNS resolution in the VPC.

Why A: Route tables must be manually updated after adding a NAT Gateway. The private subnet's route table must have a default route (0.0.0.0/0) pointing to the NAT Gateway.

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Last reviewed: Jun 20, 2026

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