Multicast traffic between VLAN and Overlay segment through edge bridge doesn't work.

Products

• VMware NSX

Issue/Introduction

- Multicast traffic connectivity issue
- Multicast traffic from VLAN side doesn't reach overlay segments
- IGMP reports from overlay VMs is not seen on the VLAN side

Environment

VMware NSX
VMware NSX Data Center

Cause

Multicast traffic over VXLAN works when all the receiver and the initiator are all on the same host. When the receiver is moved to different host then that of the multicast router / switch, the multicast joins are not forwarded to the router. 

This is because the Multicast router/switch is not aware that the ESX host where edge VM is located, is interested in this IGMP group.

Resolution

Versions where this is a known issue:
NSX-T 3.2.x, 4.1.x, 4.2.x

Workaround:

Enable the following advanced ESX config option on *ALL* ESX hosts where the overlay VMs participating in bridging are located:
Net.SendIGMPReportToUplink

This can be enabled from vCenter UI (in the Inventory view, click the ESX host --> Configure --> System --> Advanced System Settings --> click Edit and update Net.SendIGMPReportToUplink setting to 1) or through esxcli:

esxcli system settings advanced set -o "/Net/SendIGMPReportToUplink" --int-value 1