Unable to send ARP message between VMs in different subnets on the same vnet

Question

Hello, I am having trouble sending ARP messages between VM1 in subnet1 and VM2 in subnet2 on the same vnet. When I run the command "arping <target IP>" I get a timeout error. However, when I send the same message between two VMs on the same subnet, it works fine.

My understanding is that ARP works on L2 and only for local networks, which makes it seem like I can't send ARP messages across different subnets on the same vnet. Can anyone help me with this issue? Thank you.

Answer 1

Hi Barak Pahima,

In Azure ARP is not directly accessible for a Virtual Network (VNet) without any specific configuration.Because Azure operates at Layer 3 and does not support broadcast or multicast, which are used by ARP. ( https://learn.microsoft.com/en-us/azure/virtual-network/virtual-networks-faq#do-vnets-support-multicast-or-broadcast )

Besides arping tool operates at the data link layer and uses the Address Resolution Protocol (ARP) to send ARP requests to a destination host. (https://www.baeldung.com/linux/arping-command )

However, Azure provides several tools to diagnose network issues. For example, you can view Azure’s Network Watcher or the effective routes for a network interface using the Azure portal, PowerShell, or the Azure CLI2. This can help you understand how traffic is routed in your VNet.

Let me know if this information help you .

---

If the information helped address your question, please Accept the answer.