Question 601 of 969

Design security for infrastructure →hardMultiple ChoiceObjective-mapped

Quick Answer

The answer is to configure BGP on both connections and assign a higher local preference, such as 200, to routes learned via ExpressRoute. This works because BGP local preference is a weight-like attribute that influences outbound traffic from an autonomous system; Azure will always prefer the path with the highest local preference, so setting ExpressRoute routes higher than the VPN’s default of 100 ensures they are chosen when available. On the Microsoft Cybersecurity Architect exam, this scenario tests your understanding of BGP path selection for hybrid network failover, often appearing as a distractor where candidates mistakenly apply AS path prepending or MED, which affect inbound traffic, not outbound. A common trap is confusing local preference with metrics like MED or weight—remember that local preference is exchanged within an AS and is the first tiebreaker for outbound routing. Memory tip: think “Higher local pref = more preferred locally,” so ExpressRoute gets a 200 to beat the VPN’s 100.

SC-100 Design security for infrastructure Practice Question

This SC-100 practice question tests your understanding of design security for infrastructure. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 secure hybrid network architecture. They have an on-premises network connected to Azure via ExpressRoute and a site-to-site VPN as backup. They want to ensure that traffic from Azure to on-premises always uses ExpressRoute when available, but automatically fails over to VPN if ExpressRoute goes down. Which configuration should they implement?

Clue words in this question

Noticing these words before you look at the options changes how you read each choice.

Clue: "always"
Why it matters: Absolute qualifier. An answer using 'always' is only correct if there are genuinely no exceptions — absolute statements are often wrong in networking.

Question 1hardmultiple choice

Read the full VPN explanation →

A
Configure the VPN to have a lower BGP weight than ExpressRoute.
Why wrong: Lower weight would make VPN less preferred, but the scenario requires failover, not primary use.
B
Use both connections in active-active mode with BGP and rely on ECMP.
Why wrong: ECMP would load balance traffic, not provide deterministic failover.
C
Disable BGP on the VPN connection and use static routes with a higher metric for the VPN.
Why wrong: Static routes with higher metric would make VPN less preferred, but without BGP, failover might not work seamlessly.
D
Configure BGP on both connections and assign a higher local preference (e.g., 200) to routes learned via ExpressRoute.
Higher local preference makes ExpressRoute routes preferred; if ExpressRoute fails, VPN routes will be used.

Full breakdown with real-world context →

Answer choices

Why each option matters

Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.

Correct answer & explanation

✓

Configure BGP on both connections and assign a higher local preference (e.g., 200) to routes learned via ExpressRoute.

Option D is correct because BGP local preference is an attribute used to influence outbound traffic from an AS. By assigning a higher local preference (e.g., 200) to routes learned via ExpressRoute, Azure will prefer those routes over VPN routes (which default to local preference 100). This ensures that traffic from Azure to on-premises uses ExpressRoute when available, and automatically fails over to the VPN if the ExpressRoute BGP session drops, as the VPN routes will then be selected.

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.

✗
Configure the VPN to have a lower BGP weight than ExpressRoute.
Why it's wrong here
Lower weight would make VPN less preferred, but the scenario requires failover, not primary use.
✗
Use both connections in active-active mode with BGP and rely on ECMP.
Why it's wrong here
ECMP would load balance traffic, not provide deterministic failover.
✗
Disable BGP on the VPN connection and use static routes with a higher metric for the VPN.
Why it's wrong here
Static routes with higher metric would make VPN less preferred, but without BGP, failover might not work seamlessly.
✓
Configure BGP on both connections and assign a higher local preference (e.g., 200) to routes learned via ExpressRoute.
Why this is correct
Higher local preference makes ExpressRoute routes preferred; if ExpressRoute fails, VPN routes will be used.
Clue confirmation
The clue word "always" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.

Common exam traps

Common exam trap: answer the scenario, not the keyword

The trap here is that candidates often confuse BGP weight (Cisco-proprietary, local to a router) with local preference (standard, AS-wide), and incorrectly assume that lowering weight on the VPN would achieve the same result as raising local preference on ExpressRoute, but Azure does not support Cisco weight and local preference is the correct attribute for influencing outbound traffic from Azure to on-premises.

Trap categories for this question

Scenario analysis trap
Lower weight would make VPN less preferred, but the scenario requires failover, not primary use.

Detailed technical explanation

How to think about this question

BGP local preference is an AS-wide attribute that is propagated to all iBGP peers within the same AS. In Azure, when using ExpressRoute and VPN with BGP, the local preference can be set via route-maps or AS path prepending; however, local preference is the cleanest method because it is non-transitive and only affects outbound path selection. In a real-world scenario, if ExpressRoute fails, the BGP session drops, routes are withdrawn, and the VPN routes (with lower local preference) become the best path, ensuring seamless failover without manual intervention.

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

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.

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

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FAQ

Questions learners often ask

What does this SC-100 question test?

Design security for infrastructure — This question tests Design security for infrastructure — Read the scenario before looking for a memorised answer..

What is the correct answer to this question?

The correct answer is: Configure BGP on both connections and assign a higher local preference (e.g., 200) to routes learned via ExpressRoute. — Option D is correct because BGP local preference is an attribute used to influence outbound traffic from an AS. By assigning a higher local preference (e.g., 200) to routes learned via ExpressRoute, Azure will prefer those routes over VPN routes (which default to local preference 100). This ensures that traffic from Azure to on-premises uses ExpressRoute when available, and automatically fails over to the VPN if the ExpressRoute BGP session drops, as the VPN routes will then be selected.

What should I do if I get this SC-100 question wrong?

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

Are there clue words in this question I should notice?

Yes — watch for: "always". Absolute qualifier. An answer using 'always' is only correct if there are genuinely no exceptions — absolute statements are often wrong in networking.

What is the key concept behind this question?

Read the scenario before looking for a memorised answer.

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