Network traffic is being re-transmitted and not reaching destination VM.

Products

• VMware NSX

Issue/Introduction

• VM is connected to NSX Overlay Segment.
• North/South or East-West network traffic is intermittently reaching the destination VM.
• Overlay traffic from the Edge to the VM is routed to an ESXi host that is not hosting the destination VM.
• VM traffic is subsequently retransmitted between ESXi hosts.

Environment

VMware NSX 4.x

Cause

Same IP address is used on multiple VMs. An IP address conflict induces ARP flapping on the Edge, leading to inconsistent traffic routing between the affected hosts.

Resolution

You can identify IP conflicts by reviewing the Edge log file (/var/log/syslog) for ARP entries that map the same IP address to different MAC addresses.

For example, the following log entries indicate that ARP has learned the same IP on two distinct MACs (XX:XX:XX:XX:XX:XX and YY:YY:YY:YY:YY:YY):

Edge01 NSX 1365565 SWITCHING [nsx@6876 comp="nsx-edge" subcomp="datapathd" s2comp="arp" level="INFO"] ARP reply received for IP_VM from XX:XX:XX:XX:XX:XX on lrouter port PORT_ID
Edge01 NSX 1377514 SWITCHING [nsx@6876 comp="nsx-edge" subcomp="datapathd" s2comp="arp" level="INFO"] GARP reply received for IP_VM from YY:YY:YY:YY:YY:YY on lrouter port PORT_ID

To resolve this issue, locate the duplicate IP assignments in your environment and remove or reconfigure the conflicting VM or Pod.