- A
The user-defined route, because UDRs always beat BGP routes.
Why wrong: UDRs do not always win. Route selection starts with the most specific prefix, so a longer BGP prefix can be chosen first.
- B
The BGP route, because it has the more specific prefix length.
Azure route selection uses longest-prefix match before considering route source precedence. The BGP route for 172.16.10.0/24 is more specific than the UDR for 172.16.0.0/16, so the /24 route is selected for traffic to 172.16.10.20. Source precedence only matters when multiple routes have the same prefix length.
- C
The system route to the virtual network, because system routes are preferred over learned routes.
Why wrong: System routes are not preferred over a more specific learned route. They are only used when no more specific route exists.
- D
No route is chosen because Azure does not support overlapping prefixes.
Why wrong: Azure supports overlapping routes and resolves them using prefix length and source precedence. Overlap alone is not an error.
AZ-104 Implement and Manage Virtual Networking Practice Question
This AZ-104 practice question tests your understanding of implement and manage virtual networking. 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 route table contains a user-defined route for 172.16.0.0/16 to a virtual appliance. The ExpressRoute circuit advertises 172.16.10.0/24. A VM in the subnet sends traffic to 172.16.10.20. Which route does Azure use?
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
The BGP route, because it has the more specific prefix length.
Azure uses the most specific prefix match to determine the next hop. The BGP route for 172.16.10.0/24 has a longer prefix length (24) than the user-defined route for 172.16.0.0/16 (16), so the BGP route is preferred regardless of route source priority. This follows the longest prefix match (LPM) algorithm, which overrides the default preference order of UDRs over BGP routes.
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.
- ✗
The user-defined route, because UDRs always beat BGP routes.
Why it's wrong here
UDRs do not always win. Route selection starts with the most specific prefix, so a longer BGP prefix can be chosen first.
When this WOULD be correct
This option would be correct if the UDR and BGP route had the same prefix length (e.g., both /24) and the UDR was for a different prefix that still matched the destination. In that case, Azure prefers UDRs over BGP routes for equal prefix lengths.
- ✓
The BGP route, because it has the more specific prefix length.
Why this is correct
Azure route selection uses longest-prefix match before considering route source precedence. The BGP route for 172.16.10.0/24 is more specific than the UDR for 172.16.0.0/16, so the /24 route is selected for traffic to 172.16.10.20. Source precedence only matters when multiple routes have the same prefix length.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
The system route to the virtual network, because system routes are preferred over learned routes.
Why it's wrong here
System routes are not preferred over a more specific learned route. They are only used when no more specific route exists.
When this WOULD be correct
This option would be correct in a scenario where a VM sends traffic to an IP address that falls within the virtual network's address space (e.g., 10.0.0.10 in a VNet with address space 10.0.0.0/16), and there are no more specific user-defined or BGP routes. Azure then uses the system route for virtual network traffic.
- ✗
No route is chosen because Azure does not support overlapping prefixes.
Why it's wrong here
Azure supports overlapping routes and resolves them using prefix length and source precedence. Overlap alone is not an error.
When this WOULD be correct
If the question stated that the UDR and BGP route had the same prefix length (e.g., both /24) and the UDR was preferred over BGP routes by design, then option D would be incorrect; but for D to be correct, Azure would need to reject overlapping prefixes entirely, which it does not.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The AZ-104 exam frequently reuses these exact scenarios with slightly different constraints.
✓The BGP route, because it has the more specific prefix length.Correct answer▾
Why this is correct
Azure route selection uses longest-prefix match before considering route source precedence. The BGP route for 172.16.10.0/24 is more specific than the UDR for 172.16.0.0/16, so the /24 route is selected for traffic to 172.16.10.20. Source precedence only matters when multiple routes have the same prefix length.
✗The user-defined route, because UDRs always beat BGP routes.Wrong answer — click to see why▾
Why this is wrong here
Azure uses the most specific prefix match, not a fixed preference for UDRs over BGP routes. Since the BGP route (172.16.10.0/24) is more specific than the UDR (172.16.0.0/16), the BGP route is chosen.
★ When this WOULD be the correct answer
This option would be correct if the UDR and BGP route had the same prefix length (e.g., both /24) and the UDR was for a different prefix that still matched the destination. In that case, Azure prefers UDRs over BGP routes for equal prefix lengths.
Why candidates choose this
Candidates may incorrectly remember a rule that 'UDRs always override BGP routes' without considering the prefix length priority, which is the primary factor in route selection.
✗The system route to the virtual network, because system routes are preferred over learned routes.Wrong answer — click to see why▾
Why this is wrong here
System routes are preferred over learned routes only when there is no more specific route; here, the BGP route (172.16.10.0/24) is more specific than the system route (virtual network address space), so Azure uses the most specific match, which is the BGP route.
★ When this WOULD be the correct answer
This option would be correct in a scenario where a VM sends traffic to an IP address that falls within the virtual network's address space (e.g., 10.0.0.10 in a VNet with address space 10.0.0.0/16), and there are no more specific user-defined or BGP routes. Azure then uses the system route for virtual network traffic.
Why candidates choose this
Candidates may incorrectly remember that system routes are always preferred over learned routes, without understanding that route selection is based on longest prefix match first, and system routes are only preferred when prefix lengths are equal.
✗No route is chosen because Azure does not support overlapping prefixes.Wrong answer — click to see why▾
Why this is wrong here
Azure supports overlapping prefixes between UDRs and BGP routes; the more specific prefix (172.16.10.0/24) is used regardless of route source, so a route is chosen.
★ When this WOULD be the correct answer
If the question stated that the UDR and BGP route had the same prefix length (e.g., both /24) and the UDR was preferred over BGP routes by design, then option D would be incorrect; but for D to be correct, Azure would need to reject overlapping prefixes entirely, which it does not.
Why candidates choose this
Candidates may think that overlapping prefixes cause conflicts or that Azure disallows them, confusing overlapping address spaces with route selection behavior.
Analysis generated from the official AZ-104blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume UDRs always override BGP routes, but Azure applies longest prefix match first, so a more specific BGP route will be used over a less specific UDR.
Detailed technical explanation
How to think about this question
Azure uses a route selection process based on the longest prefix match (LPM) first, then route source priority (UDR > BGP > system) as a tiebreaker. In this scenario, the BGP route for 172.16.10.0/24 is more specific than the UDR for 172.16.0.0/16, so it wins. This behavior aligns with RFC 4271 for BGP and Azure's virtual network routing implementation, where overlapping prefixes are handled by prefix length, not by route source order.
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.
Visual reference
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FAQ
Questions learners often ask
What does this AZ-104 question test?
Implement and Manage Virtual Networking — This question tests Implement and Manage Virtual Networking — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The BGP route, because it has the more specific prefix length. — Azure uses the most specific prefix match to determine the next hop. The BGP route for 172.16.10.0/24 has a longer prefix length (24) than the user-defined route for 172.16.0.0/16 (16), so the BGP route is preferred regardless of route source priority. This follows the longest prefix match (LPM) algorithm, which overrides the default preference order of UDRs over BGP routes.
What should I do if I get this AZ-104 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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Last reviewed: Jun 11, 2026
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