User defined route does not work when associated despite all the vm in the same vnet. Additionally, ping is disrupted when associated to a vm.

Question

User defined route does not work when associated despite all the vm in the same vnet. Additionally, ping is disrupted when associated to a vm.

Answer 1

Hello @Shuvajit Roy ,

Welcome to Microsoft Q&A Platform. Thank you for reaching out & hope you are doing well.

I understand that you have associated UDR to a subnet but the connectivity between VMs in the same Vnet is not working. Also, you are unable to ping the VMs.

Could you please share the configuration that you want to achieve? When you say all VMs in the same Vnet, how are you routing the traffic?

Is it from VM1 (subnet1) to VM2 (subnet2) via a VM3 (subnet3)? If yes, you can refer the below doc which shows a tutorial on how to achieve this:

https://learn.microsoft.com/en-us/azure/virtual-network/tutorial-create-route-table-portal

To route traffic through a VM acting as an NVA, you need to turn on IP forwarding in Azure and in the operating system of NVA virtual machine. Once IP forwarding is enabled, any traffic received by the NVA VM that's destined for a different IP address, won't be dropped and will be forwarded to the correct destination.

Refer: https://learn.microsoft.com/en-us/azure/virtual-network/tutorial-create-route-table-portal#turn-on-ip-forwarding

To turn on IP forwarding for the operating system of NVA virtual machine to forward network traffic.

Refer: https://learn.microsoft.com/en-us/azure/virtual-network/tutorial-create-route-table-portal#turn-on-ip-forwarding-in-the-operating-system

And if you are trying to ping from one VM to another, you need to make sure that ICMP is allowed in the VM's OS Windows Firewall.

Refer: https://learn.microsoft.com/en-us/azure/virtual-network/tutorial-create-route-table-portal#allow-icmp-in-windows-firewall

NOTE: Always deploy a virtual appliance/NVA VM into a different subnet than the resources that route through the virtual appliance. Deploying the virtual appliance to the same subnet then applying a route table to the subnet that routes traffic through the virtual appliance can result in routing loops where traffic never leaves the subnet.

Refer: https://learn.microsoft.com/en-us/azure/virtual-network/virtual-networks-udr-overview#user-defined

Kindly let us know if the above helps or you need further assistance on this issue.

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