Lost access to a VM after the VM was migrated by DRS.

Products

• VMware vSphere ESXi

Issue/Introduction

• VM running running Microsoft NLB with Virtual IP (VIP).
• Multicast filtering mode was set to Basic on the DVS. 

                         

• When VMs are migrated to specific hosts , the Virtual IP in Microsoft NLB (Network Load Balancer) becomes unreachable.
• When the configuration of the host is reviewed, the multicast filtering mode is still showing as snooping: 

   #net-dvs -l |grep "multicastFilter"
                com.vmware.vswitch.multicastFilter = snooping ,         propType = CONFIG

  
  The configuration on a working host shows the multicast filtering mode as legacyFiltering (as expected) 

  #net-dvs -l |grep "multicastFilter"
                com.vmware.vswitch.multicastFilter = legacyFiltering ,         propType = CONFIG

Environment

VMware vSphere 7.x
VMware vSphere 8.x

Cause

The multicast filter change to Basic filtering made on the DVS  was not pushed correctly. The problem hosts still have the multicast filter set to Snooping. 

Resolution

1. Identify all the hosts that are using the DVS to confirm that the proxy DVS on the host  has the correct multicastFilter setting using the command:
   #net-dvs -l |grep "multicastFilter"
2. If it is showing as "snooping": 
   Put host in maintenance mode 
   Reboot the host to push the correct configuration of the DVS to the host. 

Additional Information

IGMP/MLD snooping when enabled makes Virtual IP in Microsoft NLB (Network Load Balancer) not reachable

What is Multicast Filtering