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

Products

• VMware NSX

Issue/Introduction

• 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.

Workaround:

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)