Intermittent TCP/UDP traffic loss traversing an Edge in an NSX-T environment

Products

• VMware NSX

Issue/Introduction

Symptoms:

• TCP/UDP traffic traversing an Edge appears to be dropped intermittently
• ICMP traffic is observed not to be impacted

Environment

VMware NSX-T Data Center 2.x
VMware NSX-T Data Center

Cause

Flow Cache is an optimization that helps reduce CPU cycles spent on known flows.
Flow Cache tables get populated when a new flow begins.
Decisions for other packets in an existing flow known to flow cache will use an optimized implementation (fast path) for processing.
It has been observed that intermittently the flow maybe sent to the incorrect destination TEP IP resulting in the loss of packets.

Resolution

This issue is resolved in VMware NSX-T Data Center 2.4, available at VMware Downloads.

Workaround:
To workaround this issue, please disable flow cache on the Edge machines
   #set dataplane flow-cache disabled
   #restart service dataplane (Note this will cause a brief interruption to the dataplane)