An enterprise is designing an Azure network infrastructure. The topology includes a hub vi… — Microsoft Azure Solutions Architect (AZ-305)

An enterprise is designing an Azure network infrastructure. The topology includes a hub virtual network named `vnet-weur-hub` ( $10.10.0.0/16$ ) peered with a spoke virtual network named `vnet-weur-spoke1` ( $10.20.0.0/16$ ). An active Network Virtual Appliance (NVA) is deployed in the hub virtual network in `snet-nva` ( $10.10.2.0/24$ ) with the private IP address $10.10.2.4$ .

The spoke virtual network `vnet-weur-spoke1` contains the following subnets:
* `snet-web` ( $10.20.1.0/24$ ) hosting front-end web servers.
* `snet-db` ( $10.20.2.0/24$ ) hosting database servers.

To inspect all inter-subnet traffic within the spoke, a network engineer associates a route table with `snet-web` containing a user-defined route (UDR) for $10.20.0.0/16$ pointing to the NVA at $10.10.2.4$ . However, this configuration prevents the web servers within `snet-web` from communicating with each other, breaking the application.

You need to restore communication between the web servers in `snet-web` while ensuring that all traffic from `snet-web` to `snet-db` (and any future subnets added to `vnet-weur-spoke1`) is routed through the NVA at $10.10.2.4$ . The design must minimize administrative overhead.

Which configuration should you add to the route table associated with `snet-web` to resolve the communication issue?

Add a user-defined route for $10.20.1.0/24$ with the next hop type set to Virtual network.Answer
B
Add a user-defined route for $10.20.1.0/24$ with the next hop type set to None.
C
Disable virtual network gateway route propagation on the route table.
D
Remove the route for $10.20.0.0/16$ and add a route for $10.20.2.0/24$ pointing to the NVA at $10.10.2.4$ .

Answer

Add a user-defined route for the local subnet prefix (

10.20.1.0/24

) pointing to the Virtual network next hop type.

Adding a route for the local subnet prefix (

10.20.1.0/24

) with a next hop type of Virtual network is correct because it uses the Longest Prefix Match (LPM) algorithm to override the broader

10.20.0.0/16

UDR for local traffic only. This restores communication within the subnet while continuing to route traffic destined for other subnets (such as the database subnet) to the NVA. It also satisfies the administrative requirement because any future subnets created in the spoke VNet will automatically match the broader

10.20.0.0/16

route and route to the NVA without needing manual route table modifications.

Step-by-Step Solution

Analyze the routing conflict in the route table.

The current user-defined route for

10.20.0.0/16

pointing to the NVA overrides the default VnetLocal system route (

10.20.0.0/16

-> Virtual network) because they share the same prefix length, forcing all traffic (including intra-subnet traffic) to the NVA.

By default, Azure routes traffic within a VNet locally. When a UDR with the exact same prefix length is applied, it overrides this system route, sending all traffic matching that prefix to the NVA, which cannot hair-pin the traffic back to the same subnet.

Apply the Longest Prefix Match (LPM) rule.

A route with a more specific prefix (e.g.,

10.20.1.0/24

) will take precedence over a route with a broader prefix (e.g.,

10.20.0.0/16

Azure's routing decision is based first on the prefix length. The route with the longest prefix matches first.

Configure the local subnet override.

Adding a route for

10.20.1.0/24

with the next hop set to Virtual network ensures that traffic within `snet-web` matches the /24 route and uses Azure's default local routing.

This restores intra-subnet communication while leaving the /16 route active for all other subnets within the VNet.

Evaluate administrative overhead.

Future subnets (e.g.,

10.20.3.0/24

) will automatically fall under the

10.20.0.0/16

route and route to the NVA without requiring manual route updates.

This satisfies the requirement to minimize administrative overhead as the network scales.

Key Concept

Azure routing precedence, specifically how User-Defined Routes (UDRs) interact with default system routes and the application of Longest Prefix Match (LPM) to override broad routing policies without increasing administrative overhead.

Question

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Topics

More questions from this topic