The answer is to adjust the BGP Multi-Exit Discriminator (MED) attribute on the on-premises routers, along with ensuring both VPN tunnels advertise the same prefix and that the Transit Gateway route table sees them as equal-cost paths. This works because AWS Transit Gateway supports equal-cost multi-path (ECMP) routing for VPN load balancing only when the routes are truly identical in BGP attributes, and adjusting MED on the on-premises side can make the two paths appear equally preferred to the TGW, enabling active-active distribution. On the ANS-C01 exam, this scenario tests your understanding of how BGP path selection interacts with Transit Gateway ECMP, often trapping candidates who mistakenly think AS_PATH prepending or weight settings apply here—neither is supported for TGW VPN attachments. A key memory tip: for ECMP, think “MED equals, traffic splits”—if the on-premises routers send the same prefix with equal MED values, TGW will load-balance across both VPN tunnels.
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 uses AWS Transit Gateway with multiple VPC attachments and a VPN attachment to an on-premises network. The on-premises network advertises the same prefix via two separate VPN connections for redundancy. The TGW route table shows both routes as active. Traffic from a VPC to on-premises is not load-balanced and prefers one connection. Which THREE actions would help achieve active-active load balancing? (Choose 3.)
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Configure BGP AS_PATH prepending on the preferred VPN connection to make it less preferred
Using BGP AS_PATH prepending can influence path selection, equal-cost multi-path (ECMP) routing in TGW supports load balancing across equal routes, and adjusting BGP MED can influence inbound traffic. Weight is not supported in TGW; AS_PATH prepending on both sides equally would not differentiate; using VPN static routes would not support ECMP.
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.
✓
Configure BGP AS_PATH prepending on the preferred VPN connection to make it less preferred
Why this is correct
AS_PATH prepending can make one path appear longer.
Related concept
Static NAT maps one inside address to one outside address.
✓
Enable equal-cost multi-path (ECMP) routing on the Transit Gateway route table
Static NAT maps one inside address to one outside address.
✗
Set a higher BGP weight on the less preferred connection
Why it's wrong here
Weight is Cisco proprietary and not supported on AWS VPN.
✗
Use static routes for both VPN connections instead of BGP
Why it's wrong here
Static routes do not support ECMP or dynamic load balancing.
✓
Adjust the BGP Multi-Exit Discriminator (MED) attribute on the on-premises routers
Why this is correct
MED influences inbound traffic path selection.
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 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.
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: Configure BGP AS_PATH prepending on the preferred VPN connection to make it less preferred — Using BGP AS_PATH prepending can influence path selection, equal-cost multi-path (ECMP) routing in TGW supports load balancing across equal routes, and adjusting BGP MED can influence inbound traffic. Weight is not supported in TGW; AS_PATH prepending on both sides equally would not differentiate; using VPN static routes would not support ECMP.
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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