25Gbps Intel E810 vmnic link remains down on Dell PowerEdge R770 despite configuration and SFP changes.

Products

• VMware vSphere ESXi

Issue/Introduction

• On new Dell PowerEdge R770 servers, specific 25 GBit/s vmnic interfaces show a Link Status: Down.
• The issue persists even after upgrading to the most recent Server BIOS and NIC firmware.
• Standard troubleshooting, including forcing duplex/speed or enabling auto-negotiation, does not bring the link up.
• The vmnic remains "Down" even after replacing SFPs and cables or testing with known-working switch ports.
• The link state remains Down when the server is booted into a non-ESXi operating system (e.g., Ubuntu LiveCD).

Environment

VMware vSphere ESXi

Cause

The issue is rooted in the physical layer, involving a failure in the NIC hardware, the PCIe riser/slot seating, or a localized hardware defect that prevents the physical interface from initializing, regardless of the operating system or driver in use.

Resolution

Because the failure persists across different operating systems and after standard configuration changes, the issue is not software-defined.

1. Boot the affected host into a secondary OS (e.g., Ubuntu LiveCD). If the link status remains "Down" in these environments, it confirms a physical layer issue.
2. Ensure that manual BIOS overrides (forcing 25Gbps and Disabling FEC) have been attempted as per 25Gbps Intel E810-XXV vmnic down after switch reboot.
3. If the link remains down after the above steps, contact the hardware vendor for further assistance.