VM VXLAN traffic fails on a host prepared for NSX
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VM VXLAN traffic fails on a host prepared for NSX


Article ID: 324199


Updated On:


VMware NSX Networking


  • ESXi host prepared for NSX-T Data Center
  • VMs running on the host generate VXLAN traffic based on some third party software
  • The VXLAN traffic is failing at transmit
  • On the ESXi host, the vmxnet3 driver stats show that "encap (outer) header error" is incrementing e.g.
#net-stats -l | grep VXLAN_VM
2100663515          4       0 DvsPortset-1     00:50:56:01:03:9f  VXLAN_VM

#vsish -e get /net/portsets/DvsPortset-1/ports/100663515/vmxnet3/txSummary
stats of a vmxnet3 vNIC tx queue {
   failed to split a giant tso pkt:0
   giant non-tso pkts requiring more than 1 pkt handle:0
   encap (outer) header errors:228   <<<<<
   encap (inner) tso header errors:0
   number of memory region lookup pass in Tx.:0


VMware NSX
VMware NSX-T Data Center


This issue was introduced when overlay offload functionality was added.
There are two scenarios impacted
  • VXLAN traffic is using standard VXLAN ports 4789 or 8472
  • VXLAN traffic is using non-standard VXLAN ports i.e. not 4789 or 8472


For VXLAN traffic using standard VXLAN ports, this issue has been resolved in ESXi 6.7 Patch Release ESXi670-202111001 and ESXi 7 Update 3 see VMware downloads.

For VXLAN traffic using non-standard VXLAN ports, this issue is resolved by this vmxnet3 driver fix .

This configuration is typically observed using Linux VMs, please note that the vmxnet3 driver version will be linked to the Linux kernel version. Therefore, a Linux kernel upgrade may be required to get this fix.
This issue is confirmed resolved in RHEL 8, for other OSs you may need to consult the OS vendor.

For all scenarios, both standard and non-standard VXLAN ports, this issue can be solved by disabling tunnel offload on the VM guest OS.
Note, standard network stack offloads will continue to function as normal.

#ethtool -K eth0 tx-udp_tnl-segmentation off && ethtool -K eth0 tx-udp_tnl-csum-segmentation off