Does Azure server allow spoofing source IP of UDP packet

Question

In order to test load balancer performance, I need to simulate large number of UDP packets coming from different IP address. I wrote a script to spoof source IP of these packets and run the script on Azure VM. But i can not receive any packets on another Azure server. Both servers are in same vnet. Without spoofing source IP, it has no issue to receive packet. Does Azure platform blocking spoofing source IP of UDP packet?

Answer 1

Azure has an integrated high-level security system to protect the customers from different network attack and malicious activity.

for details you can check the following threads

https://learn.microsoft.com/en-us/answers/questions/93232/ip-spoofing-attack-in-aks

https://learn.microsoft.com/en-us/answers/questions/1274172/how-to-address-network-sniffing-and-spoofing-in-az

https://learn.microsoft.com/en-us/azure/virtual-network/ip-based-access-control-list-overview

to solve your problem

Create multiple VMs within your VNet and use different tools or scripts to generate UDP traffic from each VM. This simulates a scenario with diverse source IPs while remaining within the bounds of Azure's networking rules.

or

Use specialized load testing tools designed for Azure environments. These tools can often simulate traffic from a range of IP addresses without the need for spoofing. Examples include Azure Load Testing (Preview) and JMeter with Azure plugins.

Answer 2

@ling Thank you for reaching out.

Based on your statement above

Both servers are in same vnet. Without spoofing source IP, it has no issue to receive packet. Does Azure platform blocking spoofing source IP of UDP packet?

The reason for the behavior above might be due to an NSG blocking the spoofed IP address. You can check if a NSG can be associated to the VM's Nic or the subnet is blocking this connectivity. You can use IP flow verify if any NSG is blocking the connectivity.Just FYI Azure Load Balancer is Azure's most performant Load Balancer all while keeping latency ultra-low. As documented here "Azure Load Balancer is a pass-through network load balancer. Throughput limitations are determined by the type of virtual machine in the backend pool. To learn about other network throughput related information, see Virtual Machine network throughput."

Meanwhile you can also go through this Azure Load testing feature and see if it satisfies your requirement.

You can take a look at Scenarios for deploying Azure Load Testing in a virtual network.

Hope this helps! Please let me know if the issue still persists and what were your findings from the troubleshooting steps above. Thank you!

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