VXLAN traffic may be discarded by vnic if using non-default port

Products

• VMware NSX
• VMware NSX

Issue/Introduction

This article to intended to help diagnose VXLAN-related issues and provide one possible reason for the drop of VXLAN traffic on VNIC in non-NSX environment.

 

Symptoms:

• VXLAN traffic (usually generated by container deployed on virtual machines) is dropped by the VNIC
• network traffic captured on network card within the guest os shows there're tcp and icmp traffic (though there's no response to tcp traffic so it's retransmitted a few times): 
  
  
  
  
• Network traffic captured on switch port VnicTx shows that only ICMP traffic is transmitted but not TCP traffic: 

• This is noticed from the captured packet that VXLAN traffic is sent via port 4789
• The environment is using a VDS/VSS without NSX-T installed
  
  

 

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Cause

The default ports for VXLAN traffic on ESXi: 

• 4789 in NSX-V environment 
• 8472 in non-NSX-V environment

Logic on VNIC will check the port of VXLAN traffic. If the traffic is sent via non-default port, VNIC will drop it.

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Resolution

This issue is resolved in ESXi7.0P09 (in which version both ports are added as default port for VXLAN traffic).

Workaround:

1. If possible, ask customer to use the default port for VXLAN traffic.
   
   
2. Disable checksum offload within guest OS but this would bring negative impact to performance at the same time.

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Additional Information

Impact/Risks:
VXLAN traffic will be dropped by VNIC

The bug fix is carried forward to ESXi 8.0 Update 2c.

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