Virtual Machine Fails to Reach Outside Network Due to Faulty ESXi Physical Uplink configuration

Products

• VMware vSphere ESXi 8.0

Issue/Introduction

• A newly deployed virtual machine (VM) experiences a complete loss of outbound network connectivity and is unable to reach the outside network environment.
• While other virtual machines on the same ESXi host function correctly, the problematic VM cannot ping its default gateway and it uses uplink vmnic1 while all other working VM's in the ESXI host use uplink vmnic0
• Packet captures demonstrate that ARP resolution for the default gateway is failing; ARP broadcast requests exit the physical adapter on the ESXi host, but no inbound responses return from the upstream switch.

Environment

VMware vSphere ESXi

Cause

The physical uplink interface vmnic1 or its connected upstream physical switch port is non-functional or unconfigured or failing to pass return network traffic back to the ESXi host, trapping all virtual machine traffic pinned to that specific uplink interface.

Resolution

• Make sure the physical switch port where vmnic1 is connected has the correct configuration so that the ARP response comes back to the ESXI host 
• Alternatively, as a work around, Log into the affected ESXi host CLI via SSH.
• Administratively disable the faulty uplink interface by running the following command to trigger a failover to the operational interface (vmnic0):

esxcli network nic down -n vmnic1

• Verify that virtual machine network connectivity and gateway ARP resolution are restored.
• Engage the physical infrastructure or network routing team to audit the physical switch port, VLAN trunking, and port-channel configurations bound to vmnic1 before restoring the interface.