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Question 318 of 1,705

Network Security, Compliance and Governance →easyMultiple ChoiceObjective-mapped

Restricting EC2 Outbound Internet Access to Specific Destinations Using Security Groups

This ANS-C01 practice question tests your understanding of network security, compliance and governance. 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 a public subnet containing a NAT gateway and a private subnet containing EC2 instances. The EC2 instances need to download patches from the internet. The security team wants to ensure that the EC2 instances cannot initiate outbound connections to any other internet destinations. What should the network engineer do?

A
Remove the NAT gateway and attach an Internet Gateway to the private subnet route table.
Why wrong: Wrong: This would allow all outbound traffic without restriction.
B
Attach an egress-only Internet Gateway to the VPC and route private subnet traffic to it.
Why wrong: Wrong: Egress-only IGW is for IPv6 only.
C
Configure a network ACL on the private subnet to allow outbound traffic only to the patch server's IP address.
Why wrong: Wrong: NACLs are stateless and require return traffic rules; also not as flexible as security groups.
D
Assign a security group to the EC2 instances that allows outbound HTTPS traffic only to the patch server's IP address.
Correct: Security groups can restrict outbound traffic to specific destinations.

Full breakdown with real-world context →

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

✓

Assign a security group to the EC2 instances that allows outbound HTTPS traffic only to the patch server's IP address.

Option D is correct because security groups act as a virtual firewall for EC2 instances, allowing you to specify outbound rules that restrict traffic to only the necessary destinations, such as the patch server's IP address on HTTPS. This provides granular control over outbound traffic. Option A is incorrect because removing the NAT gateway and attaching an internet gateway to the private subnet would give instances direct internet access, violating the restriction. Option B is incorrect because an egress-only internet gateway is used for IPv6 traffic only, not IPv4. Option C is incorrect because network ACLs are stateless and apply to the subnet as a whole, making them less suitable for per-instance granular control; they also require rules for return traffic, complicating the configuration.

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.

✗
Remove the NAT gateway and attach an Internet Gateway to the private subnet route table.
Why it's wrong here
Wrong: This would allow all outbound traffic without restriction.
✗
Attach an egress-only Internet Gateway to the VPC and route private subnet traffic to it.
Why it's wrong here
Wrong: Egress-only IGW is for IPv6 only.
✗
Configure a network ACL on the private subnet to allow outbound traffic only to the patch server's IP address.
Why it's wrong here
Wrong: NACLs are stateless and require return traffic rules; also not as flexible as security groups.
✓
Assign a security group to the EC2 instances that allows outbound HTTPS traffic only to the patch server's IP address.
Why this is correct
Correct: Security groups can restrict outbound traffic to specific destinations.
Related concept
CIDR notation defines the prefix length.

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.

Visual reference

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.

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FAQ

Questions learners often ask

What does this ANS-C01 question test?

Network Security, Compliance and Governance — This question tests Network Security, Compliance and Governance — CIDR notation defines the prefix length..

What is the correct answer to this question?

The correct answer is: Assign a security group to the EC2 instances that allows outbound HTTPS traffic only to the patch server's IP address. — Option D is correct because security groups act as a virtual firewall for EC2 instances, allowing you to specify outbound rules that restrict traffic to only the necessary destinations, such as the patch server's IP address on HTTPS. This provides granular control over outbound traffic. Option A is incorrect because removing the NAT gateway and attaching an internet gateway to the private subnet would give instances direct internet access, violating the restriction. Option B is incorrect because an egress-only internet gateway is used for IPv6 traffic only, not IPv4. Option C is incorrect because network ACLs are stateless and apply to the subnet as a whole, making them less suitable for per-instance granular control; they also require rules for return traffic, complicating the configuration.

What should I do if I get this ANS-C01 question wrong?

What is the key concept behind this question?

CIDR notation defines the prefix length.

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