Reverting Multicast Filtering Mode to Basic from IGMP/MLD Snooping on vSphere Distributed Switch (vDS)

Products

• VMware vSphere ESXi 7.0
• VMware vSphere ESX 8.x

Issue/Introduction

When upgrading a vSphere Distributed Switch (vDS) to version 7.0 or 8.0, the Multicast Snooping mode is enabled by default, even if it was Basic previously. While this is an efficiency feature designed to accurately direct multicast traffic, it can cause connectivity failures, packet drops, and latency for legacy multicast applications or clusters that do not utilize IGMP membership reports.

Environment

• VMware vSphere 7.0 & 8.0
• vSphere Distributed Switch (vDS )7.0 & 8.0
• F5 Load Balancer or other clusters using non-standard IGMP reporting.

 

Cause

During a vDS upgrade to version 8.0, the Multicast Filtering Mode may default to IGMP/MLD snooping. This mode requires VMs to actively send IGMP join or membership reports for the vDS to populate its forwarding table. Certain load-balanced applications and features such as F5 "Auto Last Hop" do not consistently send these reports. As a result, the vDS treats the return traffic as unknown multicast and drops the frames to prevent flooding.

Resolution

Fixed in vSphere 8.0 Update 3 and higher. 

• To download the fix, visit the Broadcom Support Portal.

If an immediate upgrade is not possible, revert the Multicast Filtering Mode to Basic:

1. Log in to the vSphere Client.
2. Navigate to Networking > Select the affected vSphere Distributed Switch.
3. Go to Configure > Settings > Properties.
4. Click Edit and select the Advanced tab.
5. Change Multicast filtering mode from IGMP/MLD snooping to Basic.
6. Click OK.

Additional Information

1. Multicast Filtering Modes
2. Understanding IP Multicast in ESXi
3. IGMP/MLD snooping when enabled makes Virtual IP in Microsoft NLB (Network Load Balancer) not reachable
4. VMware ESXi 8.0 Update 3 Release Notes. 
5. Japanese KB:https://knowledge.broadcom.com/external/article/409434
6. For assistance, see Contact Broadcom Support