Ubuntu Linux 100G DDM Interface Diagnostic Information

This guide contains practical Linux commands for checking a 100G Ethernet interface, QSFP28 transceiver information and DDM (Digital Diagnostic Monitoring) values on Ubuntu Linux.

The examples show how to verify link state, speed, FEC, optical RX/TX power, module temperature, voltage, laser bias and interface errors using ethtool and standard Linux tools.

Check 100G Link Status from Kernel Messages

For an Intel network adapter using the ice driver, check recent link events with:

This confirms that the physical link is up at 100 Gbps Full Duplex and also shows the requested and negotiated FEC state.

Check Linux Interface State

Verify the administrative and operational state of the interface:

LOWER_UP and an operstate of up confirm that Linux detects the physical carrier.

Quick Check of Transceiver and RX Optical Power

For a quick DDM check, display the transceiver vendor information and received optical power on all four optical lanes:

A 100GBASE-LR4 module uses four optical channels, so checking all four RX values is useful when troubleshooting wavelength-specific optical problems.

Check Interface Speed and Capabilities

Use ethtool to verify the negotiated speed, duplex, supported link modes and current link state:

Check Full QSFP28 DDM Information

The complete module information provides transceiver type, wavelength, distance, vendor information, temperature, voltage, TX bias, TX/RX optical power and alarm status:

Check Only the Most Important DDM Values

For daily troubleshooting, filter the module output to temperature, voltage, TX bias and optical power:

This provides a compact view of the most important QSFP28 health parameters without displaying the complete EEPROM information.

Monitor Optical Power in Real Time

Use watch to monitor RX and TX optical power while troubleshooting an unstable optical link:

This refreshes the DDM values every two seconds and is useful when moving fibers, cleaning connectors or checking intermittent optical problems.

Check Network Driver and Firmware

Display the NIC driver, firmware and PCI bus information:

For Intel E810 adapters this is useful for confirming the ice driver version and NIC firmware before troubleshooting link or transceiver compatibility issues.

Check FEC Status

Check the Forward Error Correction configuration reported by the NIC driver:

FEC is especially important on high-speed Ethernet links. Compare this information with the kernel link message when troubleshooting a FEC mismatch between two devices.

Check Interface Packet Counters

Display standard Linux packet, byte, error and drop counters:

For continuous monitoring:

Check NIC Hardware Statistics

ethtool can also display driver-specific hardware counters:

When troubleshooting a bad 100G link, filter for errors, drops, CRC, FEC and fault counters:

Increasing error or FEC-related counters can indicate a physical layer problem even when the Ethernet link remains operational.

Useful 100G Interface Diagnostic Commands

What to Check During 100G Optical Troubleshooting

Start with the physical link state and verify that the interface is running at 100 Gbps. Then check the QSFP28 module type, all four RX and TX optical channels, module temperature, laser bias and alarm flags. Finally, check FEC state and NIC hardware error counters for errors that may not cause the interface to go down.

In this example the QSFP28 module is a 100GBASE-LR4 optic, the interface is up at 100 Gbps Full Duplex, all four optical channels report RX signal, the module temperature is 57.18°C, and all reported optical and temperature alarm flags are Off.