Broadcast and Multicast Traffic looping back on uplink connected to distributed switch (vDS).

Products

• VMware vSphere ESXi

Issue/Introduction

• Traffic is looped or reflected back on the uplink (vmnic) the VM is connected to, which leads to increasing MAC moving counters, resulting in VM connectivity issues. 
• Intel 'VMDq Loopback' feature is enabled on the Network Interface Card Intel E810 with icen driver 1.12.5.0. 
• Dell 'npar_tx_switching' feature is enabled on Network Interface Card QLogic 2x25GE with qedentv driver 3.71.73.0. 
• Affected VM is connected to a portgroup on a distributed switch. 
• The identified VM, which is looping traffic back, does not have a VMware assigned MAC address, identifiable as 00:50:56:##:##:##
• When the VMs state is refreshed twice, by way of vMotion, power cycle or connect / disconnected network adapter, the VM exhibits packet loopback. 

Environment

VMware vSphere ESXi 8.0. 
VMware vSphere ESXi 7.0. 

Cause

In certain instances the NIC filter is not applied to the correct queue when Intel 'VMDq loopback', as well as Dell 'npar_tx_switching' is enabled, since these are operations performed independent of the ESXi kernel. 

Resolution

This is a condition that may occur in a VMware vSphere environment.

 

Workaround: 

1. It is recommended to disable the VMDq Loopback feature on Intel NICs, by way of cli command:  esxcli intnet misc vmdqlb -e 0 -n vmnicX
2. In driver icen 1.12.5.0 or earlier, this feature cannot be disabled. It is disabled by default in driver icen 1.14.2 or later. 
3. It is recommended to disable NIC feature 'NPAR Tx switching' by way of setting npar_tx_switching=0 (implementation is vendor dependent, please consult with hardware/nic vendor)