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?

The user-defined route, because UDRs always beat BGP routes.

UDRs do not always win. Route selection starts with the most specific prefix, so a longer BGP prefix can be chosen first.

The system route to the virtual network, because system routes are preferred over learned routes.

System routes are not preferred over a more specific learned route. They are only used when no more specific route exists.

No route is chosen because Azure does not support overlapping prefixes.

Azure supports overlapping routes and resolves them using prefix length and source precedence. Overlap alone is not an error.

What does this AZ-104 question test?

CIDR notation defines the prefix length.

What is the correct answer to this question?

The correct answer is: The BGP route, because it has the more specific prefix length. — Azure first compares the destination prefixes and selects the most specific match. In this case, 172.16.10.0/24 is longer and more specific than 172.16.0.0/16, so the BGP-advertised route wins for traffic to 172.16.10.20. Only when prefixes are equally specific does route source precedence matter, where UDR would outrank BGP and system routes. Why others are wrong: UDRs do not automatically override every other route; longest-prefix match comes first. System routes are not inherently preferred when a more specific learned route exists. Overlapping prefixes are expected in Azure networking and are resolved by normal route selection rules, not rejected outright.

What should I do if I get this AZ-104 question wrong?

Then try more questions from the same exam bank and focus on understanding why the wrong options are tempting.