Today, while troubleshooting application connectivity issues for a customer, we uncovered a problem that initially looked like an application or network issue but ultimately turned out to be a faulty ESXi network driver.
The environment was experiencing intermittent connectivity problems affecting virtual machine workloads. Users reported slow application response times, increased latency, and occasional connection instability.
After deeper analysis, the root cause was traced back to a new known issue affecting specific Broadcom NetXtreme E Series network adapters running older versions of the VMware ESXi bnxtnet driver.
The affected ESXi hosts showed several indicators of network degradation:
While the infrastructure remained operational, application performance was significantly impacted because dropped packets forced retransmissions and increased communication delays between systems.
The issue affects Broadcom NetXtreme E Series adapters using certain driver versions.
The faulty driver can lead to packet drops under load, causing network instability and degraded application performance.
When investigating packet loss in a virtualized environment, the focus is typically on:
In this case, packet captures and performance analysis revealed a growing number of retransmissions. Further investigation of the ESXi hosts uncovered RX queue related messages in the vmkernel logs pointing directly to the bnxtnet driver.
You can view ESX paketloss statistics using different approaches:
Additionally the ESXi Host's vmkernel log showed a huge amount of network driver warnings like below
This helped narrow down the root cause and avoided unnecessary troubleshooting efforts across other layers of the stack.
The recommended mitigation is straightforward:
Update the bnxtnet driver to:
Version 238.1.222.x or newer
Ensure the NIC firmware is updated to the latest version provided by your hardware vendor:
Updating both the driver and firmware is important to avoid compatibility issues and benefit from the latest stability fixes.
Broadcom provides the latest ESXi network drivers through its support portal:
Download Broadcom ESXi Drivers
Broadcom has now published an official Knowledge Base article documenting this issue:
Excessive packet drops reported on ESXi 8.0.3 with Broadcom 25Gb NICs
The publication of this KB confirms the behavior observed during customer troubleshooting and provides additional guidance for affected environments.
If your environment uses Broadcom NetXtreme E Series adapters and you are experiencing unexplained network performance issues, don't limit your investigation to the application or virtual machine layer.
Review:
A simple driver update could resolve issues that otherwise lead to lengthy and frustrating troubleshooting efforts.
As infrastructure becomes increasingly software-defined, driver quality remains a critical component of overall platform stability. Even in highly resilient VMware Cloud Foundation and vSphere environments, a faulty network driver can introduce application outages, latency, and performance degradation that are difficult to diagnose.
This case serves as a good reminder that keeping ESXi drivers and firmware up to date is just as important as patching the hypervisor itself.
At comdivision, we regularly help customers identify and resolve performance issues across VMware Cloud Foundation, vSphere, NSX, and vSAN environments. Sometimes the root cause is complex, and sometimes it's as simple as a network driver that needs an update.