Virtual Machines experience network connectivity loss after vMotion

Products

• VMware NSX

Issue/Introduction

After migrating a Virtual Machine (VM) to a destination ESXi host via vMotion, the VM experiences a complete loss of network connectivity.

Environment

VMware ESXi

Cause

The upstream physical network switch ports connected to the destination ESXi host are incorrectly configured or incomplete. Missing configuration details, such as omitted VLANs on a trunk port, prevent the Layer 2 broadcast traffic (ARP) from reaching the Default Gateway, isolating the VM at Layer 2.

A packet capture will result in repeated ARP requests when the VM is trying to reach the DGW

Resolution

 

• Identify the destination ESXi host where the VM resides and determine the active physical uplinks (vmnics) associated with the affected virtual switch or distributed switch.

• Engage the physical network administration team to inspect the upstream physical switch ports connected to the identified vmnics.

• Verify and correct the switch port configuration to ensure all required VLANs are permitted and 802.1Q trunking is properly established.

• Confirm network restoration by verifying successful ARP resolution and outbound ICMP/TCP communication from the affected VM.

 

Additional Information

To validate the condition locally on the ESXi host before engaging network teams, the pktcap-uw utility can be used on the ESXi command line to observe the outbound ARP broadcasts and the explicit lack of ingress ARP replies.

Example:

pktcap-uw --uplink vmnic"x" --capture UplinkSndKernel -o - |tcpdump-uw -r - -n host "DGW IP"

Where "x" is the number of the physical uplink found using esxtop - N