The answer is to advertise the same AS path length from both routers. This is correct because BGP’s path selection algorithm prioritizes the shortest AS path length, and when both paths have equal length, the router proceeds to tie-breaking steps like MED, local preference, and IGP metric—but with identical AS path lengths, AWS Direct Connect will load-balance inbound traffic across both connections, achieving an active-active configuration. On the AWS Certified Advanced Networking Specialty ANS-C01 exam, this question tests your understanding of BGP path selection in a multi-Direct Connect design, often hiding traps like manipulating MED or local preference, which would only affect outbound traffic or require additional complexity. The key insight is that AS path length is the first deterministic attribute after local preference, so equalizing it is the simplest way to force active-active behavior. Memory tip: “Same path, same weight—traffic splits, don’t complicate.”
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 is designing a Direct Connect solution with two connections to provide high availability. The company has two customer routers, each connected to a separate AWS Direct Connect location. The company uses BGP to advertise the same prefixes from both routers. What is the correct way to configure the BGP attributes to ensure that traffic uses both connections actively?
Advertise the same AS path length from both routers.
Equal AS path length results in equal preference, allowing active-active use.
B
Use AS path prepending on both routers to make the paths equally long.
Why wrong: AS path prepending would artificially lengthen the AS path, but if both are prepended equally, it could work, but typically prepending is used to make a path less preferred; using the natural AS path is simpler.
C
Set a higher local preference on the primary router and lower on the secondary.
Why wrong: This makes the primary route more preferred, not active-active.
D
Advertise a shorter AS path on the primary router and a longer AS path on the secondary router.
Why wrong: This makes the primary path more preferred, not active-active.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Advertise the same AS path length from both routers.
Option A is correct because advertising the same AS path length from both routers ensures that AWS Direct Connect routers see both paths as equally preferred under the BGP path selection process (which considers AS path length before MED, local preference, and IGP metric). With equal AS path length, traffic will be load-balanced across both Direct Connect connections, actively using both links for inbound traffic from AWS to the customer network.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✓
Advertise the same AS path length from both routers.
Why this is correct
Equal AS path length results in equal preference, allowing active-active use.
Related concept
Read the scenario before looking for a memorised answer.
✗
Use AS path prepending on both routers to make the paths equally long.
Why it's wrong here
AS path prepending would artificially lengthen the AS path, but if both are prepended equally, it could work, but typically prepending is used to make a path less preferred; using the natural AS path is simpler.
✗
Set a higher local preference on the primary router and lower on the secondary.
Why it's wrong here
This makes the primary route more preferred, not active-active.
✗
Advertise a shorter AS path on the primary router and a longer AS path on the secondary router.
Why it's wrong here
This makes the primary path more preferred, not active-active.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse AS path prepending as a method to achieve equal path preference, but prepending actually makes a path longer and less preferred, so using it on both routers would still result in equal but artificially inflated AS path lengths, which is unnecessary and not the standard approach for active/active use.
Detailed technical explanation
How to think about this question
In BGP path selection, AS path length is compared after local preference and before MED; equal AS path lengths lead to tie-breaking steps like MED, IGP metric, and router ID. For active/active use of Direct Connect, both connections must advertise the same prefixes with identical AS path lengths so that AWS can load-balance inbound traffic across both virtual interfaces (VIFs). Real-world implementations often use BGP communities to influence AS path prepending on the AWS side, but for equal preference, no prepending is applied.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
An e-commerce site experiences heavy traffic on Black Friday and near-zero traffic during off-peak weeks. Rather than provisioning permanent large VMs, the team uses auto-scaling groups that add capacity automatically under load and reduce it overnight. Questions like this test whether you understand elasticity, availability zones, and cloud compute scaling patterns.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Network Design — This question tests Network Design — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Advertise the same AS path length from both routers. — Option A is correct because advertising the same AS path length from both routers ensures that AWS Direct Connect routers see both paths as equally preferred under the BGP path selection process (which considers AS path length before MED, local preference, and IGP metric). With equal AS path length, traffic will be load-balanced across both Direct Connect connections, actively using both links for inbound traffic from AWS to the customer network.
What should I do if I get this ANS-C01 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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