- A
The on-premises network does not have a route to the VPC CIDR.
Why wrong: The on-premises network does have a route to the VPC CIDR (as stated in the stem), so this is not the cause.
- B
The VPC route table has a more specific route (e.g., 0.0.0.0/0) pointing to an Internet Gateway.
Why wrong: While a default route to an Internet Gateway can cause asymmetric routing for return traffic, it does not affect inbound traffic direction from on-premises to the VPC. The VPC route table only controls outbound traffic; inbound traffic is determined by the on-premises router's routing table, which depends on BGP-learned routes.
- C
The BGP session between the on-premises router and the Direct Connect router is down.
If the BGP session is down, the on-premises router cannot exchange routes with the Direct Connect router, so it loses the Direct Connect path to the VPC and falls back to internet routing. This is the most likely cause.
- D
The virtual private gateway is not attached to the VPC.
Why wrong: The virtual private gateway is attached to the VPC (as stated in the stem), so this is not the cause.
SOA-C02 BGP 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: bGP. 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 network to AWS. The SysOps team notices that traffic from the on-premises network to a VPC is not using the Direct Connect connection but instead is going over the internet. The VPC has a virtual private gateway attached and the on-premises router is advertising a specific route. 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 BGP session between the on-premises router and the Direct Connect router is down.
Option C is correct because the BGP session between the on-premises router and the Direct Connect router is down. When BGP is down, the on-premises router cannot exchange routes with the AWS side over Direct Connect. Even though the on-premises router may be advertising a specific route, without an active BGP session, that route is not received by the Direct Connect router, and the virtual private gateway does not propagate it into the VPC. As a result, traffic from the on-premises network to the VPC falls back to using the internet route instead of Direct Connect. Option B is incorrect because the VPC route table controls outbound traffic from the VPC, not inbound traffic from on-premises; a default route to an Internet Gateway would cause asymmetric routing for return traffic but would not prevent inbound traffic from using Direct Connect if the BGP session is active.
Key principle: BGP
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 on-premises network does not have a route to the VPC CIDR.
Why it's wrong here
The on-premises network does have a route to the VPC CIDR (as stated in the stem), so this is not the cause.
- ✗
The VPC route table has a more specific route (e.g., 0.0.0.0/0) pointing to an Internet Gateway.
Why it's wrong here
While a default route to an Internet Gateway can cause asymmetric routing for return traffic, it does not affect inbound traffic direction from on-premises to the VPC. The VPC route table only controls outbound traffic; inbound traffic is determined by the on-premises router's routing table, which depends on BGP-learned routes.
- ✓
The BGP session between the on-premises router and the Direct Connect router is down.
Why this is correct
If the BGP session is down, the on-premises router cannot exchange routes with the Direct Connect router, so it loses the Direct Connect path to the VPC and falls back to internet routing. This is the most likely cause.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
- ✗
The virtual private gateway is not attached to the VPC.
Why it's wrong here
The virtual private gateway is attached to the VPC (as stated in the stem), so this is not the cause.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap is that candidates often suspect VPC route misconfigurations or virtual private gateway attachment issues, but the core problem is a failed BGP session on the Direct Connect link, which stops route exchange between on-premises and AWS.
Detailed technical explanation
How to think about this question
In AWS, route tables evaluate the most specific route (longest prefix match) first; a 0.0.0.0/0 route to an Internet Gateway will match any destination not explicitly covered by a more specific route. For Direct Connect traffic to flow correctly, the VPC route table must contain a route for the on-premises CIDR (e.g., 192.168.0.0/16) pointing to the virtual private gateway, or the BGP-advertised route must be propagated into the route table via route propagation. A common misconfiguration is having a default route to an Internet Gateway that overrides the more specific Direct Connect route, especially when the on-premises CIDR is not explicitly added.
KKey Concepts to Remember
- BGP
- Direct Connect
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
BGP
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.
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 bGP, 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 — BGP.
What is the correct answer to this question?
The correct answer is: The BGP session between the on-premises router and the Direct Connect router is down. — Option C is correct because the BGP session between the on-premises router and the Direct Connect router is down. When BGP is down, the on-premises router cannot exchange routes with the AWS side over Direct Connect. Even though the on-premises router may be advertising a specific route, without an active BGP session, that route is not received by the Direct Connect router, and the virtual private gateway does not propagate it into the VPC. As a result, traffic from the on-premises network to the VPC falls back to using the internet route instead of Direct Connect. Option B is incorrect because the VPC route table controls outbound traffic from the VPC, not inbound traffic from on-premises; a default route to an Internet Gateway would cause asymmetric routing for return traffic but would not prevent inbound traffic from using Direct Connect if the BGP session is active.
What should I do if I get this SOA-C02 question wrong?
Review bGP, 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?
BGP
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Last reviewed: Jun 24, 2026
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