Intermittent disconnections reported on ESXi hosts when one host joins the network, the other loses connectivity

Products

• VMware vSphere ESX 8.x

Issue/Introduction

• Intermittent network connectivity issue was reported for two hosts within the same cluster.
• The hosts exhibited a mutual exclusive conflict where the initialization of one host's network interface would immediately cause the other to lose connectivity.
• If pings to the first host fail the moment the second host's interface was initialized this indicates a direct network collision.

Environment

VMware vSphere 8.0 U3

Cause

• This is caused by a MAC address conflict between the management interfaces (vmk0) of the affected hosts.
• Management interfaces on both hosts were assigned an identical hardware address(MAC). This caused "MAC flapping" on the physical switch, as the network infrastructure could not determine the correct destination port for the shared address.

Resolution

Delete and recreate the vmk0 interface on the conflicting host. This forces the ESXi host to assign a new, unique MAC address to the vmk0 vmkernel adapter. Once the interface is recreated, both hosts will maintain stable, simultaneous connectivity and remain fully reachable from the jump server.