Microsoft NLB Virtual IP is unreachable when IGMP/MLD snooping is enabled on vDS

Products

• VMware vSphere ESXi

Issue/Introduction

• Running Microsoft NLB with VIP on vDS
• Virtual IP in Microsoft NLB (Network Load Balancer) will not be reachable when IGMP/MLD snooping is enabled on vDS.

Environment

VMware vSphere 8.x
VMware vSphere 7.x
VMware ESXi 7.x
VMware ESXi 8.x

Cause

The IGMP snooping table needs to be built up with the IGMP join message and in Microsoft NLB, IGMP join message is not sent.
If IGMP snooping is enabled on the vDs, the virtual switch can not build the lookup table for the VIP of the NLB and packets will be dropped.
In VCF/NSX environments, the default vDS mode is often "IGMP/MLD snooping," which is a common trigger for this issue during migrations.

Resolution

NLB is not supported when IGMP/MLD snooping is enabled on vDS multicast filtering mode.
Workaround: Set multicast filtering mode (on vDs) to Basic:

1. Log in to the vSphere Client.
2. Navigate to the Networking inventory view.
3. Select the affected vSphere Distributed Switch.
4. Go to Configure > Settings > Properties.
5. Click Edit, then select the Advanced tab.
6. Locate the Multicast filtering mode and change the selection from IGMP/MLD snooping to Basic.
7. Click OK to save the changes

Additional Information

Configuring VMware vSphere ESXi Security Policies for Windows Network Load Balancing (NLB) While Minimizing Security Exposure
IGMP/MLD snooping を有効にすると、Microsoft NLB（Network Load Balancer）の仮想IPにアクセスできなくなります。