The correct answer is that local preference is not honored by AWS on BGP sessions, so you must use AS path prepending to prefer Direct Connect over VPN. AWS BGP routers ignore the local preference attribute you set on your customer router because local preference is only exchanged between iBGP peers within the same AS, not across an eBGP session with AWS. This is a common trap on the AWS Certified Advanced Networking Specialty ANS-C01 exam: candidates often assume local preference works universally, but AWS only respects AS path length for outbound traffic selection. To force traffic through Direct Connect, you prepend your own AS number multiple times on the VPN BGP advertisements, making the VPN path appear longer and thus less preferred. The exam tests your understanding that BGP attribute manipulation must align with AWS’s supported attributes. Memory tip: “AWS ignores local love, so prepend the path to defend.”
ANS-C01 Network Implementation Practice Question
This ANS-C01 practice question tests your understanding of network implementation. 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 an AWS Direct Connect connection with a private VIF to a VPC. They also have a VPN connection as a backup. They want to use BGP attributes to prefer the Direct Connect path. On the customer router, they set a lower local preference for routes received via the VPN. However, traffic still uses the VPN. What could be the reason?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Local preference is not supported by AWS for BGP sessions; use AS path prepending instead
Option D is correct because AWS does not honor local preference set by the customer; AS path prepending is the standard method. Option A is wrong because MED is used to influence inbound traffic from AWS. Option B is wrong because BFD is for fast failure detection. Option C is wrong because weight is a Cisco-proprietary attribute not used in AWS.
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.
✓
Local preference is not supported by AWS for BGP sessions; use AS path prepending instead
Why this is correct
AWS does not accept local preference; AS path prepending is used to influence outbound traffic.
Related concept
Static NAT maps one inside address to one outside address.
✗
The weight attribute is set higher on the VPN routes
Bidirectional Forwarding Detection (BFD) is not enabled on the Direct Connect connection
Why it's wrong here
BFD does not affect path selection.
✗
The BGP MED attribute is not set on the VPN routes
Why it's wrong here
MED is used for inbound traffic, not outbound.
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: Local preference is not supported by AWS for BGP sessions; use AS path prepending instead — Option D is correct because AWS does not honor local preference set by the customer; AS path prepending is the standard method. Option A is wrong because MED is used to influence inbound traffic from AWS. Option B is wrong because BFD is for fast failure detection. Option C is wrong because weight is a Cisco-proprietary attribute not used in AWS.
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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