Question 284 of 997

Security →mediumMultiple ChoiceObjective-mapped

CV0-004 Security Practice Question

This CV0-004 practice question tests your understanding of security. 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 cloud administrator needs to ensure that a set of AWS EC2 instances can only be accessed via SSH from the corporate office IP range 203.0.113.0/24. Which configuration should the administrator implement?

A
Create a security group with an inbound rule allowing TCP port 22 from 203.0.113.0/24
Security groups are stateful and can restrict inbound SSH to the specific IP range.
B
Deploy a VPN and require all SSH traffic to go through it
Why wrong: A VPN is not necessary; a security group can directly restrict access.
C
Configure a network ACL with an inbound allow rule for TCP port 22 from 203.0.113.0/24
Why wrong: Network ACLs are stateless and require separate outbound rules; security groups are more appropriate for this scenario.
D
Use AWS WAF to block SSH traffic except from 203.0.113.0/24
Why wrong: WAF operates at the application layer (HTTP/HTTPS) and does not filter SSH.

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

✓

Create a security group with an inbound rule allowing TCP port 22 from 203.0.113.0/24

A security group acts as a stateful virtual firewall for EC2 instances. By specifying the source IP range 203.0.113.0/24 on the inbound SSH rule, only traffic from that range is allowed. Security groups are stateful, so return traffic is automatically permitted.

Key principle: ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.

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 security group with an inbound rule allowing TCP port 22 from 203.0.113.0/24
Why this is correct
Security groups are stateful and can restrict inbound SSH to the specific IP range.
Related concept
Standard ACLs match source addresses.
✗
Deploy a VPN and require all SSH traffic to go through it
Why it's wrong here
A VPN is not necessary; a security group can directly restrict access.
✗
Configure a network ACL with an inbound allow rule for TCP port 22 from 203.0.113.0/24
Why it's wrong here
Network ACLs are stateless and require separate outbound rules; security groups are more appropriate for this scenario.
✗
Use AWS WAF to block SSH traffic except from 203.0.113.0/24
Why it's wrong here
WAF operates at the application layer (HTTP/HTTPS) and does not filter SSH.

Common exam traps

Common exam trap: ACLs stop at the first match

ACLs are processed top to bottom. The first matching entry wins, and an implicit deny usually exists at the end.

Trap categories for this question

Scenario analysis trap
Network ACLs are stateless and require separate outbound rules; security groups are more appropriate for this scenario.

Detailed technical explanation

How to think about this question

ACL questions test precision: source, destination, protocol, port and direction. A generally correct ACL can still fail if it is applied on the wrong interface or in the wrong direction.

KKey Concepts to Remember

Standard ACLs match source addresses.
Extended ACLs can match source, destination, protocol and ports.
The first matching ACL entry is used.
There is usually an implicit deny at the end.

TExam Day Tips

Check inbound versus outbound direction.
Read the ACL from top to bottom.
Look for a broader permit or deny above the intended line.

Key takeaway

ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.

Real-world example

How this comes up in practice

A security administrator must allow nursing staff to reach a patient records server while blocking access from the guest Wi-Fi VLAN. After applying an extended ACL, traffic is still blocked from nursing workstations. The ACL was applied outbound instead of inbound on the wrong interface. Questions like this test ACL direction and placement rules.

What to study next

Got this wrong? Here's your next step.

Review ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related CV0-004 ACL questions on filtering logic and placement.

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FAQ

Questions learners often ask

What does this CV0-004 question test?

Security — This question tests Security — Standard ACLs match source addresses..

What is the correct answer to this question?

The correct answer is: Create a security group with an inbound rule allowing TCP port 22 from 203.0.113.0/24 — A security group acts as a stateful virtual firewall for EC2 instances. By specifying the source IP range 203.0.113.0/24 on the inbound SSH rule, only traffic from that range is allowed. Security groups are stateful, so return traffic is automatically permitted.

What should I do if I get this CV0-004 question wrong?

What is the key concept behind this question?

Standard ACLs match source addresses.

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Last reviewed: Jul 4, 2026

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