The answer is to configure two virtual interfaces and use BGP to advertise the same prefixes with equal metrics, enabling ECMP load balancing across both Direct Connect VIFs. This works because BGP ECMP (Equal-Cost Multi-Path) allows a router to forward traffic over multiple equal-cost paths simultaneously, distributing the load across the two VIFs when the same network prefixes are advertised with identical AS-path length and MED values. On the AWS Certified Advanced Networking Specialty ANS-C01 exam, this scenario tests your understanding of how to achieve high availability and bandwidth utilization with Direct Connect, often appearing as a trap where candidates mistakenly choose static routes or VPN overlays—static routes lack native load balancing, and VPNs add unnecessary overhead. A key memory tip: think “same prefix, same metric, ECMP magic” to recall that BGP must see the routes as equal-cost for load balancing to occur.
ANS-C01 Network Design Practice Question
This ANS-C01 practice question tests your understanding of network design. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 VPC with multiple subnets across two AZs. The VPC is connected to an on-premises data center via AWS Direct Connect. The company wants to ensure that traffic between the VPC and on-premises is load-balanced across two Direct Connect virtual interfaces (VIFs) for high availability. Which configuration should be used?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Configure two VIFs and use BGP to advertise the same prefixes with equal metrics to enable ECMP.
Option D is correct because using BGP routing with equal-cost multipath (ECMP) across two VIFs allows traffic to be load-balanced. Option A is wrong because a single VIF is a single point of failure. Option B is wrong because static routes do not provide load balancing; one route is typically preferred. Option C is wrong because a VPN over the VIFs adds overhead and does not provide native load balancing.
Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
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 two VIFs and use BGP to advertise the same prefixes with equal metrics to enable ECMP.
Common exam trap: usable hosts are not the same as total addresses
Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.
Detailed technical explanation
How to think about this question
Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.
KKey Concepts to Remember
CIDR notation defines the prefix length.
Block size helps identify subnet boundaries.
Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
The required host count determines the smallest suitable subnet.
TExam Day Tips
→Write the block size before choosing the subnet.
→Check whether the question asks for hosts, subnets or a specific address range.
→Do not confuse /24, /25, /26 and /27 host counts.
Key takeaway
Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
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 block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related ANS-C01 subnetting questions on CIDR, address ranges, and subnet selection.
Network Design — This question tests Network Design — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: Configure two VIFs and use BGP to advertise the same prefixes with equal metrics to enable ECMP. — Option D is correct because using BGP routing with equal-cost multipath (ECMP) across two VIFs allows traffic to be load-balanced. Option A is wrong because a single VIF is a single point of failure. Option B is wrong because static routes do not provide load balancing; one route is typically preferred. Option C is wrong because a VPN over the VIFs adds overhead and does not provide native load balancing.
What should I do if I get this ANS-C01 question wrong?
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related ANS-C01 subnetting questions on CIDR, address ranges, and subnet selection.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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Question Discussion
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