- A
Disable equal-cost multipath (ECMP) routing on the Transit Gateway.
Why wrong: Incorrect. AWS Transit Gateway does not allow disabling ECMP; ECMP is always enabled for equal-cost paths.
- B
Create VPC peering connections between all VPCs.
Why wrong: Incorrect. VPC peering connections do not resolve asymmetric routing through a Transit Gateway; they provide direct connectivity between VPCs but do not influence path selection.
- C
Use BGP ASN prepending on the on-premises routers.
Correct. BGP ASN prepending on the on-premises routers makes the VPN path appear less preferred due to a longer AS path, breaking ECMP and ensuring symmetric routing.
- D
Enable route propagation from the Transit Gateway to VPC route tables.
Why wrong: Incorrect. Enabling route propagation simply adds routes to VPC route tables and does not affect ECMP behavior or path selection.
Resolve Asymmetric Routing in Transit Gateway by Disabling ECMP
This ANS-C01 practice question tests your understanding of network management and operations. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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 company has a transit gateway with multiple VPC attachments and an on-premises VPN connection. The network team is seeing asymmetric routing and packet drops. What should they implement to resolve this?
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
Use BGP ASN prepending on the on-premises routers.
Option C is correct because BGP ASN prepending on the on-premises routers can influence the path selection by making one path less preferred, thereby breaking the equal-cost multipath (ECMP) behavior that causes asymmetric routing. AWS Transit Gateway does not support disabling ECMP; it always uses ECMP for equal-cost paths. By prepending ASN, the on-premises side advertises routes with a longer AS path, making the VPN path less attractive and forcing all traffic through a single preferred path, resolving asymmetry. Option A is incorrect because AWS Transit Gateway does not allow ECMP to be disabled. Option B is incorrect because VPC peering does not address routing through a Transit Gateway. Option D is incorrect because route propagation simply advertises routes and does not affect ECMP behavior.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Disable equal-cost multipath (ECMP) routing on the Transit Gateway.
Why it's wrong here
Incorrect. AWS Transit Gateway does not allow disabling ECMP; ECMP is always enabled for equal-cost paths.
- ✗
Create VPC peering connections between all VPCs.
Why it's wrong here
Incorrect. VPC peering connections do not resolve asymmetric routing through a Transit Gateway; they provide direct connectivity between VPCs but do not influence path selection.
- ✓
Use BGP ASN prepending on the on-premises routers.
- ✗
Enable route propagation from the Transit Gateway to VPC route tables.
Why it's wrong here
Incorrect. Enabling route propagation simply adds routes to VPC route tables and does not affect ECMP behavior or path selection.
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
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
- Use explanations to understand the rule behind the answer.
TExam Day Tips
- Underline the problem statement mentally.
- 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
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A startup's cloud architect reviews their monthly bill and notices costs are higher than expected for a long-running batch job. Switching from on-demand instances to Reserved Instances — or using Spot/Preemptible VMs — can reduce compute costs by up to 72 %. Questions like this test whether you understand the tradeoffs between commitment, flexibility, and cost across cloud pricing models.
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.
Identify which ANS-C01 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
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FAQ
Questions learners often ask
What does this ANS-C01 question test?
Network Management and Operations — This question tests Network Management and Operations — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Use BGP ASN prepending on the on-premises routers. — Option C is correct because BGP ASN prepending on the on-premises routers can influence the path selection by making one path less preferred, thereby breaking the equal-cost multipath (ECMP) behavior that causes asymmetric routing. AWS Transit Gateway does not support disabling ECMP; it always uses ECMP for equal-cost paths. By prepending ASN, the on-premises side advertises routes with a longer AS path, making the VPN path less attractive and forcing all traffic through a single preferred path, resolving asymmetry. Option A is incorrect because AWS Transit Gateway does not allow ECMP to be disabled. Option B is incorrect because VPC peering does not address routing through a Transit Gateway. Option D is incorrect because route propagation simply advertises routes and does not affect ECMP behavior.
What should I do if I get this ANS-C01 question wrong?
Identify which ANS-C01 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 20, 2026
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