An Azure administrator configures three virtual networks in the East US region as follows:… — Microsoft Azure Administrator (AZ-104)

An Azure administrator configures three virtual networks in the East US region as follows:

* VNet1 ( $10.10.0.0/16$ ) contains a subnet named Subnet1 ( $10.10.1.0/24$ ) with a virtual machine named VM1 ( $10.10.1.4$ ).
* VNet2 ( $10.20.0.0/16$ ) contains a subnet named Subnet2 ( $10.20.1.0/24$ ) with a virtual machine named VM2 ( $10.20.1.4$ ).
* VNet3 ( $10.30.0.0/16$ ) contains a subnet named Subnet3 ( $10.30.1.0/24$ ) with a virtual machine named VM3 ( $10.30.1.4$ ).

The administrator establishes the following configuration:

1. Virtual network peering is configured between VNet1 and VNet2. The peering settings are:
* Peering from VNet1 to VNet2: 'Allow forwarded traffic' is enabled; 'Use remote gateways' is disabled.
* Peering from VNet2 to VNet1: 'Allow forwarded traffic' is enabled; 'Allow gateway transit' is disabled.
2. Virtual network peering is configured between VNet2 and VNet3. The peering settings are:
* Peering from VNet2 to VNet3: 'Allow forwarded traffic' is enabled; 'Allow gateway transit' is disabled.
* Peering from VNet3 to VNet2: 'Allow forwarded traffic' is enabled; 'Use remote gateways' is disabled.
3. IP forwarding is enabled on the network interface of VM2, and the operating system inside VM2 is configured to route traffic (functioning as a Network Virtual Appliance).
4. A route table named RT1 is created with a user-defined route for prefix $10.30.0.0/16$ pointing to the private IP address of VM2 ( $10.20.1.4$ ) as the Next Hop. RT1 is associated with Subnet1.

Based on this scenario, is the statement that VM1 can establish a successful bidirectional ping with VM3 true or false?

Cevap: Cevap

Cevap

The statement is false because network communication requires bidirectional pathing, and there is no return route configured on Subnet3 for traffic destined to VNet1.

The correct answer is that the statement is false. Bidirectional traffic flow requires both outbound and inbound routing configurations to be complete. Since virtual network peering is non-transitive, VNet3 cannot reach VNet1 directly. Without a user-defined route on Subnet3 directing return traffic to the network virtual appliance (VM2), the ping response packets are dropped at the destination subnet.

Adım Adım Çözüm

Evaluate the outbound route from the source virtual machine.

VM1 sends an ICMP echo request to VM3 (

10.30.1.4

). The request matches the user-defined route in route table RT1 associated with Subnet1. The route directs the packet to the next hop VM2 (

10.20.1.4

) in VNet2.

To verify if the outbound packet correctly leaves Subnet1 and identifies its next hop.

Evaluate the forwarding capability of the Network Virtual Appliance (NVA).

VM2 receives the packet. Since IP forwarding is enabled on its network interface, it accepts the packet and processes it for routing. Because VNet2 is directly peered with VNet3, VM2 utilizes the system route for VNet3 (

10.30.0.0/16

via VNet peering) and successfully forwards the packet to VM3 (

10.30.1.4

To verify if the NVA can forward the transit packet across the peering link to the destination virtual network.

Evaluate the return route from the destination virtual machine.

VM3 receives the ICMP echo request and attempts to send a reply back to VM1 (

10.10.1.4

). VM3 checks the routing table of Subnet3. Because virtual network peering is non-transitive, VNet3 has system routes only for its own space and directly peered spaces (VNet2), but not for VNet1. Without a user-defined route on Subnet3 for

10.10.0.0/16

, VM3 has no path to VM1.

To verify if the destination subnet has the necessary routing information to return traffic to the source network.

Determine the final bidirectional connectivity status.

The return packet is dropped at Subnet3, preventing the bidirectional ping from completing successfully.

To conclude the status of the connection based on the analysis of both directions.

Anahtar Kavram

Azure virtual network peering is non-transitive, and configuring custom transit routing requires User-Defined Routes (UDRs) on all participating subnets to establish bidirectional communication paths.

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