How to Resolve Azure Network Configuration Issue for Routing VM Traffic to Internet through another VM

Question

Hello, I am currently facing a network configuration challenge on Microsoft Azure, and I'm seeking assistance in resolving the issue. I have set up two Windows virtual machines in one subnet, and another Windows virtual machine (VM-Gateway) in a separate subnet. The goal is to route outgoing traffic from the two VM Windows through VM-Gateway to the Internet. I have activated the Routing and Remote Access Service (RRAS) on VM-Gateway, but unfortunately, I haven't been successful in configuring it to achieve the desired routing. I've also configured a User Defined Route (UDR) to redirect all traffic (0.0.0.0/0) to the IP address of VM-Gateway, and the VM-Gateway has been set up with functional Internet access. Despite these efforts, the traffic from the VM Windows does not seem to be passing through VM-Gateway to the Internet as intended. I have reviewed the configurations of VM-Gateway, routes, and Network Security Groups (NSGs), but I'm unable to pinpoint the issue. If anyone has experience with RRAS or insights into what might be causing issues in my configuration, I would greatly appreciate any assistance or advice you could provide. Thank you in advance for your valuable help!

Answer 1

Hi @Philippe DA SILVA OLIVEIRA,

did you select Enable IP forwarding on the VM-Gateway VM in the network settings?

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(If the reply was helpful please don't forget to upvote and/or accept as answer, thank you)

Regards

Andreas Baumgarten

Answer 2

Hello @Philippe DA SILVA OLIVEIRA ,

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

I understand that you are trying to route traffic from your Azure VMs to Internet via a NVA machine in another subnet but even after adding UDR and enabling IP forwarding, the traffic is not going through.

You can refer the below tutorial with a similar setup to understand the requirements and how it works:

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

Since you mentioned that the UDR is already in place and the VM-Gateway already has IP forwarding enabled, the only thing I could think of is that IP forwarding is not enabled in the VM's operating system.

As mentioned in the below doc:

While IP forwarding is an Azure setting, the VM must also run an application that's able to forward the traffic, such as a firewall, WAN optimization, or load balancing application.

Refer: https://learn.microsoft.com/en-us/azure/virtual-network/virtual-network-network-interface?tabs=azure-portal#enable-or-disable-ip-forwarding

You mentioned that you've activated the Routing and Remote Access Service (RRAS) on VM-Gateway, but I would request you to validate if the RRAS server has the IPv4 forwarding enabled.

1. Right-click Routing and Remote Access, and then click Properties.
2. On the IPv4 tab, select Enable IPv4 Forwarding, and then click OK to save your changes.

Refer: https://learn.microsoft.com/en-us/archive/msdn-technet-forums/ce1d2eb2-248f-4130-9975-2f8882a8a4f9

https://forsenergy.com/en-us/rras/html/3fc0d556-8b4c-4dda-af53-f45efe87c91e.htm

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

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Answer 3

Hello, Thank you for your assistance. I had indeed enabled the IP forwarding on Windows as well. I solved my issue by adding a second network card to my VM. The configuration on the Routing and Remote Access Service was done automatically, and it now works. Regards, Philippe DA SILVA OLIVEIRA