- A
The security group on the EC2 instances blocks outbound ICMP
Why wrong: The security group on the EC2 instances allows all ICMP traffic, and security groups are stateful, meaning outbound traffic is permitted if the corresponding inbound traffic was allowed. Therefore, outbound ICMP from the EC2 instances is not blocked by the security group.
- B
The network ACL for the private subnet blocks outbound traffic
Why wrong: The network ACL (NACL) for the private subnet is stateless and requires explicit rules for inbound and outbound traffic. However, the default NACL allows all outbound traffic, and the administrator has not modified it to block ICMP. Hence, the NACL is not blocking outbound ICMP.
- C
The on-premises network does not have a route back to the VPC CIDR through the Direct Connect
The on-premises servers need a route back to the VPC CIDR through the Direct Connect. Since they can ping the EC2 instances, traffic from on-premises to VPC is working, but the return traffic may be going through the internet if the on-premises route is not configured, causing the ping failure from EC2 to on-premises.
- D
The VPC route table does not have a route to the on-premises CIDR via the virtual private gateway
Why wrong: The stem states that the VPC route table has a route to the on-premises CIDR via the virtual private gateway, so this option is incorrect.
SOA-C02 Direct Connect Practice Question
This SOA-C02 practice question tests your understanding of networking and content delivery. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. A key principle to apply: direct Connect. 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 uses AWS Direct Connect to connect its on-premises data center to a VPC. The VPC has a private subnet with EC2 instances that need to communicate with on-premises servers. The on-premises network team reports that they can ping the EC2 instances, but the EC2 instances cannot ping the on-premises servers. The SysOps administrator checks the route tables and finds that the VPC has a route to the on-premises CIDR via the virtual private gateway. The security groups allow all ICMP traffic. What is the most likely cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"most likely"Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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
The on-premises network does not have a route back to the VPC CIDR through the Direct Connect
Option C is correct because if the on-premises servers can ping EC2 instances, traffic from on-premises to VPC is working. However, for EC2 to ping on-premises, the return traffic from on-premises must route back through Direct Connect. If the on-premises network lacks a route back to the VPC CIDR over Direct Connect, the traffic may go through the internet, causing the ping to fail. Option A is incorrect because the security groups are configured to allow all ICMP traffic, so outbound ICMP is not blocked. Option B is incorrect because the default network ACL allows all outbound traffic, and if a custom NACL were blocking outbound, it would need explicit deny rules; typically, this is not the most likely cause. Option D is incorrect because the VPC route table already has a route to the on-premises CIDR via the virtual private gateway, as stated in the scenario.
Key principle: Direct Connect
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The security group on the EC2 instances blocks outbound ICMP
Why it's wrong here
The security group on the EC2 instances allows all ICMP traffic, and security groups are stateful, meaning outbound traffic is permitted if the corresponding inbound traffic was allowed. Therefore, outbound ICMP from the EC2 instances is not blocked by the security group.
- ✗
The network ACL for the private subnet blocks outbound traffic
- ✓
The on-premises network does not have a route back to the VPC CIDR through the Direct Connect
Why this is correct
The on-premises servers need a route back to the VPC CIDR through the Direct Connect. Since they can ping the EC2 instances, traffic from on-premises to VPC is working, but the return traffic may be going through the internet if the on-premises route is not configured, causing the ping failure from EC2 to on-premises.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Direct Connect
- ✗
The VPC route table does not have a route to the on-premises CIDR via the virtual private gateway
Common exam traps
Common exam trap: answer the scenario, not the keyword
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Detailed technical explanation
How to think about this question
Treat this as a scenario question. Identify the problem, the constraint, and the best action. Then compare each option against those facts.
KKey Concepts to Remember
- Direct Connect
- Asymmetric Routing
- Security Group
- Network ACL
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
Direct Connect
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.
Visual reference
Quick reference
Asymmetric Encryption Algorithm Comparison
| Algorithm | Key Exchange | Signatures | Equivalent Security Key | Notes |
|---|---|---|---|---|
| RSA-3072 | Yes | Yes | 128-bit | Widely deployed; slow for bulk data |
| ECDSA P-256 | No | Yes | 128-bit | Fast signatures; standard TLS certs |
| ECDH / ECDHE | Yes | No | 128-bit | Perfect forward secrecy in TLS 1.3 |
| DH / DHE | Yes | No | 128-bit (3072-bit key) | Replaced by ECDHE in modern TLS |
| Ed25519 | No | Yes | ~128-bit | SSH keys, modern PKI |
What to study next
Got this wrong? Here's your next step.
Review direct Connect, then practise related SOA-C02 questions on the same topic to reinforce the concept.
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Networking and Content Delivery — study guide chapter
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FAQ
Questions learners often ask
What does this SOA-C02 question test?
Networking and Content Delivery — This question tests Networking and Content Delivery — Direct Connect.
What is the correct answer to this question?
The correct answer is: The on-premises network does not have a route back to the VPC CIDR through the Direct Connect — Option C is correct because if the on-premises servers can ping EC2 instances, traffic from on-premises to VPC is working. However, for EC2 to ping on-premises, the return traffic from on-premises must route back through Direct Connect. If the on-premises network lacks a route back to the VPC CIDR over Direct Connect, the traffic may go through the internet, causing the ping to fail. Option A is incorrect because the security groups are configured to allow all ICMP traffic, so outbound ICMP is not blocked. Option B is incorrect because the default network ACL allows all outbound traffic, and if a custom NACL were blocking outbound, it would need explicit deny rules; typically, this is not the most likely cause. Option D is incorrect because the VPC route table already has a route to the on-premises CIDR via the virtual private gateway, as stated in the scenario.
What should I do if I get this SOA-C02 question wrong?
Review direct Connect, then practise related SOA-C02 questions on the same topic to reinforce the concept.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Direct Connect
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Last reviewed: Jun 20, 2026
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