VM vMotion creates Packet Loop Issues when using Cisco Nexus Switches

Products

• VMware vSphere ESXi
• VMware NSX
• VMware NSX-T Data Center

Issue/Introduction

When a VM has vMotion performed that causes the vNic of VMs running on other hosts not involved in that vMotion on the same vSwitch to send SSDP packets to the host switch causing a packet loop on the virtual switch when a Cisco Nexus switch is used

Environment

VMware NSX-T Data Center

VMware NSX

Cause

The topology is configured for LACP by using lag as teaming which causes a mirror on vMotion for destination hosts. When Multicast snooping is enabled after vMotion of VMs, the host switch will loop the SSDP packets with MAC address of VMs running on other hosts that are not involved in vMotion. The vSwitch then forwards incoming SSDP packets back out to the external network/switches.

 

Resolution

Workaround:

Change multicast filter mode from snooping to legacy or block SSDP packets (port 1900)

Additional Information

Impact/Risks:

When multicast filtering is set to Multicast Snooping SSDP traffic is initiated during vMotion from the vNIC of a VM on another host to the vSwitch that causes VMs not involved in vMotion to send SSDP packets to the virtual switch which will then forward incoming SSDP packets back out to the external network.