UDP Packet Drops Observed on Avi Service Engines with RSS Enabled

Products

• VMware Avi Load Balancer

Issue/Introduction

Packet drops are observed on an Avi Virtual Service under the following conditions:

• The Virtual Service is configured with a UDP Network Profile.
• Receive Side Scaling (RSS) is enabled on the Service Engine Group.
• The deployment is on a VMware vCenter or NSX-T environment.

Bug ID: AV-256987

Cause

This issue occurs due to a configuration gap regarding the VMXNET3 adapter settings on the Service Engine VM.

By default, UDP RSS is not enabled on the underlying VM network interfaces, even if RSS is enabled in the Avi SE Group configuration.

To resolve this, the parameter ethernetX.udpRSS = "1" must be explicitly defined in the VM Advanced Parameters for every interface. 

Resolution

The requirement for manual configuration depends on the Avi Controller version and the deployment state of the Service Engine (SE).

Avi Version 30.2.7 and Later:

• New Deployments: Service Engines newly deployed on VMware and NSX clouds automatically include the correct UDP RSS settings. No manual action is required.
• Upgraded SEs: Service Engines upgraded from versions prior to 30.2.7 do not automatically acquire these settings. You must apply the manual configuration steps below.

Avi Version 30.2.6 and Earlier:

• All Service Engines require the manual configuration steps below.

 

Manual Configuration Steps:

To enable UDP RSS on existing or upgraded Service Engines, modify the VM configuration in vCenter.

This change must be applied to all network interfaces (vmxnet3 adapters) present on the Service Engine VM.

1. Log in to the vSphere Client (vCenter).
2. Power off the target Service Engine VM.
3. Right-click the VM and select Edit Settings.
4. Navigate to Advanced Parameters.
5. Add the following parameter for every network interface present (where X corresponds to the interface number):

1. Attribute: ethernetX.udpRSS

2. Value: 1

1. Example configuration for a VM with 10 interfaces:

2. ethernet0.udpRSS = "1"
   ethernet1.udpRSS = "1"
   ...
   ethernet9.udpRSS = "1"
   

3. Click OK to save the parameters.
4. Power On the Service Engine VM.

Example configuration screenshot from the VM settings:

 

Additional Information

RSS KB: https://techdocs.broadcom.com/us/en/vmware-security-load-balancing/avi-load-balancer/avi-load-balancer/30-2/se-advanced-networking/configuring-tso-gro-rss-.html