The answer is to allow BGP to install both routes, as AWS will automatically load balance across them using ECMP. This works because AWS supports equal cost multipath (ECMP) only when BGP routes are learned from different Direct Connect connections with the same AS path length and identical prefix, which occurs here when both on-premises routers advertise 10.0.0.0/8. On the AWS Certified Advanced Networking Specialty ANS-C01 exam, this scenario tests your understanding that Direct Connect ECMP BGP load balancing is automatic when routes are equal-cost, and a common trap is assuming you need to manually configure weights or use a VPN—neither is required. Remember, ECMP across Direct Connect requires the same prefix and AS path, not different prefixes or manipulated weights. Memory tip: “Same prefix, same path, ECMP is automatic—no math.”
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 a CIDR of 10.0.0.0/16 and needs to connect to two on-premises locations via AWS Direct Connect. Each Direct Connect connection uses a private VIF. The company wants to use BGP to exchange routes. The on-premises routers advertise the same prefix 10.0.0.0/8 for both connections. How should the network engineer configure the VPC route tables to ensure traffic is load balanced across both Direct Connect connections?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Allow BGP to install both routes; AWS will automatically load balance across them using ECMP.
AWS supports equal cost multipath (ECMP) only when BGP routes are learned from different Direct Connect connections but with the same AS path length and prefix. Since both on-premises advertise the same prefix with identical AS path, AWS will install two equal-cost routes and load balance (ECMP) across them. Option A is correct. Option B is incorrect because using a VPN would not use Direct Connect. Option C is incorrect because weight-based routing requires different weights. Option D is incorrect because AWS does not support ECMP across different prefixes.
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.
✗
Create a VPN connection over the Direct Connect and use BGP with different metrics.
Why it's wrong here
This is unnecessary and adds complexity.
✗
Create two separate route tables and associate each with half the subnets.
Why it's wrong here
This would not load balance traffic; each subnet would use only one connection.
✗
Use AWS Transit Gateway with equal cost multipath routing.
Why it's wrong here
Transit Gateway does not change ECMP behavior; Direct Connect still installs routes in the VPC route table.
✓
Allow BGP to install both routes; AWS will automatically load balance across them using ECMP.
Why this is correct
When identical routes are learned from two Direct Connect connections, AWS uses 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: Allow BGP to install both routes; AWS will automatically load balance across them using ECMP. — AWS supports equal cost multipath (ECMP) only when BGP routes are learned from different Direct Connect connections but with the same AS path length and prefix. Since both on-premises advertise the same prefix with identical AS path, AWS will install two equal-cost routes and load balance (ECMP) across them. Option A is correct. Option B is incorrect because using a VPN would not use Direct Connect. Option C is incorrect because weight-based routing requires different weights. Option D is incorrect because AWS does not support ECMP across different prefixes.
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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