Question 956 of 1,152

Security Architecture →mediumMultiple ChoiceObjective-mapped

Quick Answer

The correct answer is a stateful security group that allows inbound traffic from the ALB’s security group only. This works because stateful security groups in AWS can reference another security group as a source, meaning any traffic originating from an instance attached to the ALB’s security group is automatically permitted, while all other inbound traffic is implicitly denied. This satisfies the requirement that web servers accept traffic exclusively from the ALB, and because security groups are stateful, return traffic is allowed without additional rules. On the Security+ SY0-701 exam, this scenario tests your understanding of cloud network segmentation and the difference between stateful and stateless controls—a common trap is choosing a stateless network ACL, which cannot reference security groups and would require manually allowing ephemeral return ports. Remember the key distinction: security groups are stateful and support logical references; network ACLs are stateless and rule-based. Memory tip: “SG = Source Group” — if you can name the source group, use a security group.

SY0-701 Security Architecture Practice Question

This SY0-701 practice question tests your understanding of security architecture. 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 security architect is designing the network security for a web application hosted in a public cloud environment such as AWS. The application uses an Application Load Balancer (ALB) that distributes traffic to a fleet of web servers. The web servers must only accept traffic from the ALB, and all other inbound traffic must be blocked. The ALB itself needs to accept HTTP/HTTPS traffic from anywhere on the internet. Which of the following cloud security controls should the architect configure on the web servers' network interface to best meet this requirement, assuming the cloud provider offers both stateful and stateless network filtering options?

Clue words in this question

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

Clue: "best"
Why it matters: Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.

Question 1mediummultiple choice

Full question →

A
A stateless network ACL that allows inbound traffic from the ALB's subnet only.
Why wrong: Stateless network ACLs require explicit rules for both inbound and outbound traffic. This adds administrative complexity and is more prone to misconfiguration than a stateful security group. While it could work, it is not the best practice for this requirement because security groups offer a simpler, stateful solution that can reference the ALB's security group directly.
B
A stateful security group that allows inbound traffic from the ALB's security group only.
Correct. Security groups are stateful and can use another security group as a source. This configuration cleanly allows only traffic originating from the ALB, automatically handles return traffic, and is the recommended cloud-native approach for controlling instance-level access.
C
A web application firewall (WAF) that inspects all traffic for SQL injection.
Why wrong: A WAF inspects HTTP/HTTPS traffic at the application layer to detect and block attacks like SQL injection or cross-site scripting. It does not control network-level access or filter traffic based on source IP/security group; it is a complementary security control, not a replacement for network-layer filtering.
D
A host-based firewall on each web server that allows traffic from the ALB's private IP address.
Why wrong: A host-based firewall can be used, but it requires manual configuration on each server and does not leverage the cloud provider's built-in security group functionality. It is also harder to manage at scale compared to security groups, making it a less optimal choice for this scenario.

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

✓

A stateful security group that allows inbound traffic from the ALB's security group only.

Option B is correct because a stateful security group in AWS can reference another security group as a source, allowing inbound traffic only from instances associated with the ALB's security group. This ensures that web servers accept traffic exclusively from the ALB, while the ALB itself can accept HTTP/HTTPS from the internet via its own security group rules. Stateful filtering automatically allows return traffic, simplifying rule management and meeting the requirement precisely.

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.

✗
A stateless network ACL that allows inbound traffic from the ALB's subnet only.
Why it's wrong here
Stateless network ACLs require explicit rules for both inbound and outbound traffic. This adds administrative complexity and is more prone to misconfiguration than a stateful security group. While it could work, it is not the best practice for this requirement because security groups offer a simpler, stateful solution that can reference the ALB's security group directly.
✓
A stateful security group that allows inbound traffic from the ALB's security group only.
Why this is correct
Correct. Security groups are stateful and can use another security group as a source. This configuration cleanly allows only traffic originating from the ALB, automatically handles return traffic, and is the recommended cloud-native approach for controlling instance-level access.
Clue confirmation
The clue word "best" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
A web application firewall (WAF) that inspects all traffic for SQL injection.
Why it's wrong here
A WAF inspects HTTP/HTTPS traffic at the application layer to detect and block attacks like SQL injection or cross-site scripting. It does not control network-level access or filter traffic based on source IP/security group; it is a complementary security control, not a replacement for network-layer filtering.
✗
A host-based firewall on each web server that allows traffic from the ALB's private IP address.
Why it's wrong here
A host-based firewall can be used, but it requires manual configuration on each server and does not leverage the cloud provider's built-in security group functionality. It is also harder to manage at scale compared to security groups, making it a less optimal choice for this scenario.

Common exam traps

Common exam trap: answer the scenario, not the keyword

The trap here is that candidates often confuse stateless network ACLs with stateful security groups, assuming a subnet-based ACL is sufficient, but they overlook that ACLs cannot filter by security group and require bidirectional rule management, making them unsuitable for this precise ALB-only access requirement.

Trap categories for this question

Scenario analysis trap
A host-based firewall can be used, but it requires manual configuration on each server and does not leverage the cloud provider's built-in security group functionality. It is also harder to manage at scale compared to security groups, making it a less optimal choice for this scenario.

Detailed technical explanation

How to think about this question

Under the hood, AWS security groups act as a virtual firewall at the instance level, using a stateful connection tracking mechanism that automatically permits reply traffic for allowed inbound flows. When you specify a source security group (e.g., sg-xxxxx for the ALB), the rule is evaluated based on the private IP addresses of instances associated with that group, not the subnet. This allows granular control even across Availability Zones, whereas network ACLs operate at the subnet boundary and are stateless, requiring manual outbound rules for ephemeral ports (1024-65535) to handle return traffic.

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 security analyst at a medium-sized enterprise encounters this scenario during an investigation or architecture review. The correct answer reflects best practice for the specific threat or control described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Security exam questions test whether you can match controls to threats in context — not just recall definitions.

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.

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FAQ

Questions learners often ask

What does this SY0-701 question test?

Security Architecture — This question tests Security Architecture — Read the scenario before looking for a memorised answer..

What is the correct answer to this question?

The correct answer is: A stateful security group that allows inbound traffic from the ALB's security group only. — Option B is correct because a stateful security group in AWS can reference another security group as a source, allowing inbound traffic only from instances associated with the ALB's security group. This ensures that web servers accept traffic exclusively from the ALB, while the ALB itself can accept HTTP/HTTPS from the internet via its own security group rules. Stateful filtering automatically allows return traffic, simplifying rule management and meeting the requirement precisely.

What should I do if I get this SY0-701 question wrong?

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

Are there clue words in this question I should notice?

Yes — watch for: "best". Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.

What is the key concept behind this question?

Read the scenario before looking for a memorised answer.

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