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Difficulty: HardVirtual Network Connectivity and Routing

An organization is designing a hybrid network in Azure to support dynamic routing between their on-premises datacenter (192.168.0.0/16192.168.0.0/16) and Azure resources.

The architecture consists of the following components:
- A hub virtual network named `vnet-useast-hub-transit` (10.30.0.0/1610.30.0.0/16) that hosts an Azure Route Server named `ars-useast` in the dedicated `RouteServerSubnet`, an ExpressRoute gateway, and two active-active Network Virtual Appliances (NVAs) that establish BGP sessions with the Route Server.
- A spoke virtual network named `vnet-useast-spoke-prod` (10.40.0.0/1610.40.0.0/16) that hosts application workloads.
- A virtual network peering connection between `vnet-useast-hub-transit` and `vnet-useast-spoke-prod`.

The routing requirements are as follows:
- BGP routes from the on-premises datacenter must propagate dynamically to the virtual machines in `vnet-useast-spoke-prod` via the NVAs.
- Static User-Defined Routes (UDRs) must not be configured or managed in `vnet-useast-spoke-prod` to avoid operational overhead.
- Traffic must route dynamically between the ExpressRoute gateway and the NVAs.

Which two configuration settings should you implement to meet these requirements? (Choose two.)

  1. Enable the branch-to-branch setting on the Azure Route Server `ars-useast`.Answer
  2. Configure the virtual network peering from `vnet-useast-spoke-prod` to `vnet-useast-hub-transit` to use the remote virtual network's gateway or Route Server.Answer
  3. C
    Disable route propagation on the route tables associated with the subnets in `vnet-useast-spoke-prod`.
  4. D
    Create user-defined routes (UDRs) in `vnet-useast-spoke-prod` pointing to the private IP addresses of the NVAs as the next hop.
  5. E
    Associate a route filter with the ExpressRoute circuit targeting the private peering IP addresses of the NVAs.

Answer

To meet the routing requirements, you must enable the branch-to-branch setting on the Azure Route Server `ars-useast` to allow dynamic route exchange between the ExpressRoute gateway and the NVAs, and configure the virtual network peering from the spoke VNet to the hub VNet to use the remote virtual network's gateway or Route Server.
To establish dynamic routing between the ExpressRoute gateway and the NVAs, the branch-to-branch setting must be enabled on the Azure Route Server. This allows the Route Server to transit routes between the virtual network gateway and the BGP-enabled NVAs. Additionally, to propagate these dynamically learned routes to the spoke virtual network without using static routes, the virtual network peering from the spoke VNet to the hub VNet must be configured to use the remote virtual network's gateway or Route Server.

Step-by-Step Solution

1
Enable dynamic routing between the ExpressRoute gateway and the NVAs.
Dynamic route propagation is established between on-premises and the NVAs.
By default, Azure Route Server does not route traffic directly between gateways. Enabling the branch-to-branch setting allows the Route Server to transit routes between the ExpressRoute gateway and the NVA BGP peers.
2
Enable route propagation from the hub VNet to the spoke VNet.
The spoke virtual network learns the routes advertised by the Azure Route Server in the hub.
Configuring the virtual network peering from the spoke to use the remote virtual network's gateway or Route Server allows the spoke subnets to dynamically inherit routes from the hub Route Server.

Key Concept

Azure Route Server enables dynamic BGP route propagation across peered VNets and gateways using the branch-to-branch setting without requiring manual user-defined routes.
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Topics

Virtual Network Connectivity and Routing

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