ANS-C01 Network Design Practice Question
A company uses AWS Direct Connect with a private VIF to connect its data center to a VPC. The VPC has multiple subnets. The on-premises network team reports that they can ping the VPC's private IP addresses but cannot connect to an EC2 instance's port 443. The EC2 instance's security group allows HTTPS from the on-premises CIDR. What should the engineer check NEXT?
⚠ Common exam trap
Many candidates assume security group rules are the only firewall layer, overlooking the instance's OS firewall, which can independently block specific ports even when Layer 3 connectivity (ICMP) works.
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
✓
Check the EC2 instance's operating system firewall (e.g., iptables, Windows Firewall) to see if port 443 is blocked.
Since the on-premises team can ping the EC2 instance (ICMP works) but cannot connect to port 443 (HTTPS), the network path is functional at Layer 3. The security group already allows HTTPS from the on-premises CIDR, so the next logical step is to check the EC2 instance's OS-level firewall (e.g., iptables, Windows Firewall), which operates at Layer 4 and can independently block TCP port 443 even when the security group permits it.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Check the security group's inbound rules for port 443.
Why it's wrong here
Already checked and allowed.
- ✗
Confirm that the Direct Connect virtual interface is in the 'up' state.
Why it's wrong here
Ping works, so the interface is up.
- ✓
Check the EC2 instance's operating system firewall (e.g., iptables, Windows Firewall) to see if port 443 is blocked.
Why this is correct
OS firewall can block even if security group allows.
- ✗
Verify that the route tables in the VPC have a route back to the on-premises CIDR.
Why it's wrong here
Ping works, so routing is fine.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This ANS-C01 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the ANS-C01 exam.