Error: ESXi physical NIC reports 1G speed after 10G switch upgrade

Products

• VMware vSphere ESXi

Issue/Introduction

An ESXi host physical network adapter (vmnic) continues to report a link speed of 1Gbps (1000 Mbps) even after the connected physical switch has been upgraded to 10Gbps.

This typically occurs when physical layer components or negotiation settings are incompatible with the higher speed.

• esxcli network nic list shows "Speed" as 1000.
• vSphere Client reports "1 Gbps" under Physical Adapters.
• Manually setting the speed to 10000 Mbps fails or results in a "Link Down" status.
• Auto-negotiation is enabled on both the switch and ESXi host, but settles at 1Gbps.

Environment

VMware ESX

Cause

The link speed is limited by one of the following:

1. Physical Transceiver Limitation: The SFP/SFP+ transceiver installed in the ESXi host or switch port only supports a maximum speed of 1Gbps/1.25Gbps.
2. Cable Compatibility: The physical cabling does not support 10Gbps throughput over the required distance.
3. Negotiation Mismatch: Fixed speed settings on one end prevent the other end from successfully negotiating 10Gbps.

Resolution

1. Verify Physical Hardware Capabilities

Inspect the physical transceiver (SFP) module installed in the ESXi host:

1. Identify the model number of the transceiver.
2. Consult the hardware vendor's datasheet to confirm it supports 10Gbps (SFP+). Standard SFP modules are typically limited to 1.25Gbps.
3. Replace the module with a certified 10Gbps SFP+ transceiver if it is found to be a 1G-only module.

2. Check Driver and Firmware

Ensure the network adapter driver and firmware are compliant with the VMware Compatibility Guide (VCG).

1. Run the command: esxcli network nic get -n vmnicX to check the current driver and firmware.
2. Compare these versions against the VMware Compatibility Guide.

3. Review Switch and Host Configuration

1. Ensure the physical switch port is configured for Auto-Negotiation or explicitly set to 10Gbps.
2. In the ESXi host, ensure the vmnic is set to Auto-Negotiate. Avoid forcing 10Gbps unless the switch port is also forced to match.