This SCS-C02 practice question tests your understanding of infrastructure 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 company is deploying a web application on Amazon EC2 instances in an Auto Scaling group behind an Application Load Balancer (ALB). The instances are in a private subnet. How should the security group for the EC2 instances be configured?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Allow inbound HTTP/HTTPS from the security group of the ALB.
Option A is correct because the security group should allow HTTP/S traffic from the ALB's security group, which is a best practice for least privilege. Option B is wrong because allowing all IPs exposes instances to direct internet traffic. Option C is wrong because the ALB is in a public subnet, not the VPC CIDR. Option D is wrong because the instances are in a private subnet and should not receive traffic from the internet.
Key principle: Authentication proves identity; authorization controls what that identity can do after login. Both must work for full privileged access.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Allow inbound HTTP/HTTPS from the internet gateway.
Why it's wrong here
The internet gateway is not a source; traffic comes from IPs.
✓
Allow inbound HTTP/HTTPS from the security group of the ALB.
Why this is correct
This restricts traffic to only the ALB.
Related concept
Authentication checks who the user is.
✗
Allow inbound HTTP/HTTPS from 0.0.0.0/0.
Why it's wrong here
This would allow direct internet access, defeating the purpose of a private subnet.
✗
Allow inbound HTTP/HTTPS from the VPC CIDR.
Why it's wrong here
The ALB is not necessarily within the VPC CIDR; it has its own IP addresses.
Common exam traps
Common exam trap: authentication is not authorization
Logging in proves the user can authenticate. It does not automatically mean the user is allowed to enter privileged or configuration mode. Watch for AAA authorization, privilege level and command authorization details.
Detailed technical explanation
How to think about this question
This kind of question is testing the difference between identity and permission. A user may successfully log in to a router because authentication is working, but still fail to enter configuration mode because authorization is missing, misconfigured or mapped to a lower privilege level.
KKey Concepts to Remember
Authentication checks who the user is.
Authorization controls what the user is allowed to do after login.
Privilege levels affect access to EXEC and configuration commands.
AAA, TACACS+ and RADIUS can separate login success from command access.
TExam Day Tips
→Do not assume successful login means full administrative access.
→Look for words such as cannot enter configuration mode, privilege level, authorization or command access.
→Separate login problems from permission problems before choosing the answer.
Key takeaway
Authentication proves identity; authorization controls what that identity can do after login. Both must work for full privileged access.
Real-world example
How this comes up in practice
A healthcare organisation deploys an application with a public-facing web tier and a private database tier. The database subnet has no public IP and only accepts connections from the web tier's security group. Questions like this test whether you can design cloud network isolation using VNets/VPCs, subnets, and security group rules.
What to study next
Got this wrong? Here's your next step.
Review Cisco AAA concepts — authentication, authorization, and accounting. Study privilege levels (0–15), command authorization under TACACS+, and how RADIUS differs. Then practise related SCS-C02 questions on access control and AAA configuration.
Infrastructure Security — This question tests Infrastructure Security — Authentication checks who the user is..
What is the correct answer to this question?
The correct answer is: Allow inbound HTTP/HTTPS from the security group of the ALB. — Option A is correct because the security group should allow HTTP/S traffic from the ALB's security group, which is a best practice for least privilege. Option B is wrong because allowing all IPs exposes instances to direct internet traffic. Option C is wrong because the ALB is in a public subnet, not the VPC CIDR. Option D is wrong because the instances are in a private subnet and should not receive traffic from the internet.
What should I do if I get this SCS-C02 question wrong?
Review Cisco AAA concepts — authentication, authorization, and accounting. Study privilege levels (0–15), command authorization under TACACS+, and how RADIUS differs. Then practise related SCS-C02 questions on access control and AAA configuration.
What is the key concept behind this question?
Authentication checks who the user is.
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Question Discussion
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