Multicast and broadcast traffic looping back to VMs when using DVS

Products

• VMware vSphere ESXi

Issue/Introduction

• Aruba Virtual Mobility Controller VM 
• In a scenario where there is only one uplink on the DVS (no teaming) 
• If the VM sends either multicast or broadcast packets, it also receives the same packets it just sent itself causing a loop. 
• NPAR is configured on the host
• QLogic FastLinQ QL41xxx  card is in use (using qendtv driver)
• Packet captures taken on the uplink will see a VRRP packet being sent from the VM 
• We then see the same packet being received by the vmnic.
• The time difference between the packets is less that .00001 sec  which would likely indicate that the packet is being sent by the vmnic itself. 

Environment

ESXI 7.0.x

Cause

The qedentv NPAR configuration has an option which can cause looping within the vmnic.

 

Resolution

Disabling npar_tx_switching means there won't be internal packet forwarding (within Firmware/Hardware) between the PFs from the same physical port. 
This means that the the packet will always go to wire.

# esxcfg-module -s ‘npar_tx_switching=0’ qedentv

# reboot

 

Additional Information

NPAR Limitations of QLogic FastLinQ 45XXX and 41XXX Adapters