This ANS-C01 practice question tests your understanding of network implementation. 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 company has a Direct Connect connection with a private VIF to a VPC. They also have a Site-to-Site VPN connection to the same VPC as a backup. The on-premises router is advertising the same prefixes over both connections. The company wants to ensure that traffic uses Direct Connect when available and fails over to VPN if Direct Connect goes down. Which configuration should be applied?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Prepend AS path on the BGP advertisements over the VPN connection to make the path less preferred.
To prefer Direct Connect over VPN, you should adjust the BGP attributes on the on-premises router. One common method is to prepend AS path on the VPN BGP advertisements to make the path longer, so the Direct Connect path is preferred. Option A is correct. Option B is incorrect because decreasing the MED on Direct Connect would make it more preferred, but the question asks for a method that can be applied on-premises. Option C is incorrect because local preference is usually set on the AWS side. Option D is incorrect because disabling BGP on the VPN would remove the backup.
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.
✗
Set a higher MED value on the Direct Connect BGP advertisements.
Why it's wrong here
Higher MED makes the path less preferred; you want Direct Connect to be more preferred, so lower MED or higher on VPN.
✗
Disable BGP on the VPN connection to force traffic to Direct Connect.
Why it's wrong here
This would remove the backup VPN, not provide failover capability.
✓
Prepend AS path on the BGP advertisements over the VPN connection to make the path less preferred.
Why this is correct
AS path prepending makes the VPN path longer, so Direct Connect path (shorter AS path) is preferred.
Related concept
Static NAT maps one inside address to one outside address.
✗
Set a higher local preference on the VPN BGP advertisements.
Why it's wrong here
Higher local preference makes the path more preferred, which is opposite of desired.
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 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 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 Implementation — This question tests Network Implementation — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: Prepend AS path on the BGP advertisements over the VPN connection to make the path less preferred. — To prefer Direct Connect over VPN, you should adjust the BGP attributes on the on-premises router. One common method is to prepend AS path on the VPN BGP advertisements to make the path longer, so the Direct Connect path is preferred. Option A is correct. Option B is incorrect because decreasing the MED on Direct Connect would make it more preferred, but the question asks for a method that can be applied on-premises. Option C is incorrect because local preference is usually set on the AWS side. Option D is incorrect because disabling BGP on the VPN would remove the backup.
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.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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Question Discussion
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