Network Flapping on ESXi 8.0 U3 for RHEL 6.x VMs

Products

• VMware vSphere ESXi

Issue/Introduction

After migrating a Virtual Machine (VM) from ESXi 6.x to ESXi 8.0 U3, customers may observe the following symptoms with VM OS's that are running RHEL 6.x:

• Network connectivity flaps or intermittent packet loss.
• Load balancer (e.g., F5 Big-IP) pool members frequently drop packets or change status between 'Up' and 'Down'.
• WireShark captures show clear packet drops or communication interruptions specifically for these migrated workloads.

Environment

VMware ESXi 8.0 U3
Red Hat Enterprise Linux (RHEL) 6.10  
RHEL kernel version: 2.6.32-504.el6 (typically associated with RHEL 6.6) or lower

Cause

The issue is caused by a kernel-level incompatibility. While the Guest OS may be updated to RHEL 6.10 (which is supported), the underlying kernel may still be running version 2.6.32-504.el6. This specific kernel version, originally part of the RHEL 6.6 distribution, experiences stability issues on the ESXi 8.0 U3 networking stack.

Resolution

To resolve this issue, upgrade the guest operating system kernel to version 2.6.32-754.el6 or newer to match the RHEL 6.10 distribution standards.

Steps to Verify and Fix:

1. Log in to the affected VM.
2. Verify the current kernel version by running the following command:
   uname -r


3. Check the Red Hat release version:
   cat /etc/redhat-release


4. If the kernel is 2.6.32-504.el6 despite being on RHEL 6.10, perform a kernel update via yum or your local repository management tool:
   sudo yum update kernel


5. Reboot the VM to initialize the new kernel.
6. Verify the update was successful by re-running command: 
   uname -r


7. Monitor the network for stability.