- A
Add a route in VPC-A's subnet route table pointing to the VPC Peering connection for VPC-B's CIDR
Why wrong: Routes are typically already added; this is a basic step often done initially.
- B
Configure VPC Peering as a transit gateway
Why wrong: VPC Peering does not support transitive routing; a Transit Gateway is needed for that.
- C
Verify that VPC-B does not have a VPN connection to an on-premises network
VPC Peering does not support transitive routing; if VPC-B uses a VPN, traffic from VPC-A cannot route to on-premises.
- D
Ensure the VPC Peering connection is in the 'active' state
The peering must be accepted and active for traffic to flow.
- E
Check the Network ACLs in both VPCs to ensure inbound/outbound ICMP traffic is allowed
Network ACLs are stateless; ICMP must be allowed in both directions.
Quick Answer
The answer is to check the Network ACLs in both VPCs to ensure inbound and outbound ICMP traffic is allowed. This is correct because Network ACLs are stateless, meaning they require explicit rules for both inbound and outbound traffic; even if security groups permit ICMP, a default deny-all NACL will silently drop ping packets. In the AWS Certified SysOps Administrator Associate SOA-C02 exam, this scenario tests your understanding of the layered security model and common VPC peering connectivity troubleshooting pitfalls—specifically that route tables and security groups may look fine while a stateless NACL blocks the traffic. A frequent trap is assuming security group rules alone guarantee connectivity, forgetting that NACLs operate at the subnet level. For memory, remember that NACLs are “stateless and ruthless”—they check both directions independently, so always verify inbound and outbound ICMP rules on both sides of the peering connection.
SOA-C02 Networking and Content Delivery 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. 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 SysOps administrator is troubleshooting connectivity between two VPCs (VPC-A and VPC-B) connected via a VPC Peering connection. An EC2 instance in VPC-A cannot ping an EC2 instance in VPC-B. The route tables and security groups are correctly configured. Which THREE steps should the administrator take to resolve the issue?
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
Verify that VPC-B does not have a VPN connection to an on-premises network
Option A, Option C, and Option E are correct. VPC Peering does not support transitive routing (Option A), so a VPN Gateway is needed for on-premises connectivity. Option C: Network ACLs are stateless and may block ICMP; allowing inbound/outbound ICMP is necessary. Option E: Check that the VPC Peering connection is in the 'active' state; if not, accept the request. Option B is wrong because VPC Peering does not support transitive routing. Option D is wrong because VPC Peering does not support transitive routing.
Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Add a route in VPC-A's subnet route table pointing to the VPC Peering connection for VPC-B's CIDR
Why it's wrong here
Routes are typically already added; this is a basic step often done initially.
- ✗
Configure VPC Peering as a transit gateway
Why it's wrong here
VPC Peering does not support transitive routing; a Transit Gateway is needed for that.
- ✓
Verify that VPC-B does not have a VPN connection to an on-premises network
- ✓
Ensure the VPC Peering connection is in the 'active' state
Why this is correct
The peering must be accepted and active for traffic to flow.
Related concept
CIDR notation defines the prefix length.
- ✓
Check the Network ACLs in both VPCs to ensure inbound/outbound ICMP traffic is allowed
Common exam traps
Common exam trap: usable hosts are not the same as total addresses
Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.
Detailed technical explanation
How to think about this question
Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.
KKey Concepts to Remember
- CIDR notation defines the prefix length.
- Block size helps identify subnet boundaries.
- Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
- The required host count determines the smallest suitable subnet.
TExam Day Tips
- Write the block size before choosing the subnet.
- Check whether the question asks for hosts, subnets or a specific address range.
- Do not confuse /24, /25, /26 and /27 host counts.
Key takeaway
Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
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 block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related SOA-C02 subnetting questions on CIDR, address ranges, and subnet selection.
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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 — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: Verify that VPC-B does not have a VPN connection to an on-premises network — Option A, Option C, and Option E are correct. VPC Peering does not support transitive routing (Option A), so a VPN Gateway is needed for on-premises connectivity. Option C: Network ACLs are stateless and may block ICMP; allowing inbound/outbound ICMP is necessary. Option E: Check that the VPC Peering connection is in the 'active' state; if not, accept the request. Option B is wrong because VPC Peering does not support transitive routing. Option D is wrong because VPC Peering does not support transitive routing.
What should I do if I get this SOA-C02 question wrong?
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related SOA-C02 subnetting questions on CIDR, address ranges, and subnet selection.
What is the key concept behind this question?
CIDR notation defines the prefix length.
About these practice questions
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Same concept, more angles
2 more ways this is tested on SOA-C02
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A SysOps Administrator is setting up a VPC peering connection between two VPCs (VPC-A and VPC-B) in different AWS accounts. After the peering connection is accepted, instances in VPC-A cannot ping instances in VPC-B. Both VPCs have non-overlapping CIDR blocks. What is the MOST likely cause?
medium- ✓ A.The route tables in both VPCs do not have routes to the peer VPC CIDR.
- B.VPC peering does not support cross-account connections.
- C.The CIDR blocks overlap, causing routing conflicts.
- D.The security groups in VPC-B do not allow inbound ICMP traffic from VPC-A.
Why A: The most likely cause is that the route tables in both VPCs do not have routes to the peer VPC CIDR. Even after a VPC peering connection is accepted, traffic cannot flow between the VPCs unless explicit routes are added to each VPC's route table pointing to the CIDR block of the peer VPC, with the VPC peering connection as the target. Without these routes, instances in VPC-A have no path to reach instances in VPC-B, so ping fails.
Variation 2. A SysOps administrator is troubleshooting connectivity issues between two VPCs in different AWS Regions. Both VPCs are connected via a VPC Peering connection. The route tables in both VPCs have routes pointing to the peering connection. Security groups allow all traffic. However, an EC2 instance in VPC A cannot ping an EC2 instance in VPC B. What is the most likely cause?
hard- A.The network ACLs in subnets are blocking ICMP traffic.
- B.VPC Peering is not supported across AWS Regions.
- ✓ C.The route tables in the subnets where the instances reside do not include a route to the peered VPC's CIDR.
- D.The security groups do not allow traffic from the peered VPC's security group ID.
Why C: Option D is correct because VPC Peering does not support transitive routing; each VPC must have explicit routes to the other VPC's CIDR. If the route tables are correctly configured, the issue is likely that the instances do not have the other VPC's CIDR in their route tables. Option A is incorrect because VPC Peering works across regions. Option B is incorrect because the security groups can reference each other if the peered VPC's CIDR is added, but not by security group ID across regions. Option C is incorrect because NACLs are stateless and need rules for both directions.
Last reviewed: Jun 20, 2026
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