The answer is that the consumer receives an AccessDenied error because only the service provider account can accept a cross-account VPC endpoint service connection, not the consumer. The ec2:AcceptVpcEndpointConnections action is designed to be called by the provider who owns the endpoint service, while the consumer’s role is limited to creating the VPC endpoint and waiting for provider approval. Even if the provider’s IAM policy explicitly allows the action for a specific consumer endpoint, that policy governs the provider’s permissions, not the consumer’s. On the AWS Certified Advanced Networking Specialty ANS-C01 exam, this question tests your understanding of the separation of duties in cross-account VPC endpoint service acceptance—a common trap is assuming the consumer can self-accept. Remember the key distinction: the provider accepts, the consumer requests. A useful memory tip is “Provider Pushes, Consumer Waits”—the provider must initiate the acceptance, and the consumer cannot bypass this control.
ANS-C01 Network Design Practice Question
This ANS-C01 practice question tests your understanding of network design. 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 Network Engineer is troubleshooting a cross-account VPC endpoint connection. The service provider account (123456789012) has the above IAM policy attached to the endpoint service. The consumer account (111111111111) has created a VPC endpoint (vpce-abc123) and is trying to accept the connection. The consumer receives an 'AccessDenied' error when calling ec2:AcceptVpcEndpointConnections. 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.
The policy action should be 'ec2:CreateVpcEndpoint' instead.
Why wrong: CreateVpcEndpoint is for creating endpoints, not accepting connections.
B
The policy condition 'aws:SourceArn' does not match the consumer's endpoint ARN.
Why wrong: The condition matches the consumer's endpoint, but the issue is not about matching.
C
The policy resource ARN is incorrect; it should be the endpoint service ARN.
Why wrong: The resource is for the VPC endpoint, but the action is performed by the provider, so the resource should be the endpoint service? Actually, the action AcceptVpcEndpointConnections is on the endpoint service, not the endpoint. The resource should be the endpoint service. However, the error is likely due to permissions, not resource. But the most direct cause is that the consumer cannot accept; the provider must accept.
D
The consumer account does not have permission to accept the connection; only the service provider can accept.
The AcceptVpcEndpointConnections API is called by the service provider, not the consumer. The consumer must wait for the provider to accept.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The consumer account does not have permission to accept the connection; only the service provider can accept.
Option D is correct. The policy allows the ec2:AcceptVpcEndpointConnections action, but that action is performed by the service provider, not the consumer. The consumer needs to create the endpoint, but the acceptance is done by the provider. The error likely occurs because the consumer does not have permission to call AcceptVpcEndpointConnections on the provider's endpoint service. The policy in the provider account allows the provider to accept connections from the specified consumer endpoint. However, the consumer is trying to accept the connection themselves, which is not allowed. The provider must accept the connection using the provider account. Alternatively, the consumer might be trying to modify the endpoint to auto-accept, but that requires permissions. The most likely cause is that the consumer is attempting to accept the connection, but only the provider can accept. So the answer is D: The consumer does not have the required permissions to accept the connection on the provider's endpoint service.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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 policy action should be 'ec2:CreateVpcEndpoint' instead.
Why it's wrong here
CreateVpcEndpoint is for creating endpoints, not accepting connections.
✗
The policy condition 'aws:SourceArn' does not match the consumer's endpoint ARN.
Why it's wrong here
The condition matches the consumer's endpoint, but the issue is not about matching.
✗
The policy resource ARN is incorrect; it should be the endpoint service ARN.
Why it's wrong here
The resource is for the VPC endpoint, but the action is performed by the provider, so the resource should be the endpoint service? Actually, the action AcceptVpcEndpointConnections is on the endpoint service, not the endpoint. The resource should be the endpoint service. However, the error is likely due to permissions, not resource. But the most direct cause is that the consumer cannot accept; the provider must accept.
✓
The consumer account does not have permission to accept the connection; only the service provider can accept.
Why this is correct
The AcceptVpcEndpointConnections API is called by the service provider, not the consumer. The consumer must wait for the provider to accept.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Static NAT maps one inside address to one outside address.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
→Identify inside and outside interfaces first.
→Check whether the scenario needs static NAT, dynamic NAT or PAT.
→Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Real-world example
How this comes up in practice
A company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
What to study next
Got this wrong? Here's your next step.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related ANS-C01 NAT questions on configuration and troubleshooting.
Network Design — This question tests Network Design — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: The consumer account does not have permission to accept the connection; only the service provider can accept. — Option D is correct. The policy allows the ec2:AcceptVpcEndpointConnections action, but that action is performed by the service provider, not the consumer. The consumer needs to create the endpoint, but the acceptance is done by the provider. The error likely occurs because the consumer does not have permission to call AcceptVpcEndpointConnections on the provider's endpoint service. The policy in the provider account allows the provider to accept connections from the specified consumer endpoint. However, the consumer is trying to accept the connection themselves, which is not allowed. The provider must accept the connection using the provider account. Alternatively, the consumer might be trying to modify the endpoint to auto-accept, but that requires permissions. The most likely cause is that the consumer is attempting to accept the connection, but only the provider can accept. So the answer is D: The consumer does not have the required permissions to accept the connection on the provider's endpoint service.
What should I do if I get this ANS-C01 question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related ANS-C01 NAT questions on configuration and troubleshooting.
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?
Static NAT maps one inside address to one outside address.
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