networking system_error ai_generated partial

ethtool: Link detected: no (autonegotiation failed) on eth0

ID: networking/ethtool-autoneg-failure

Also available as: JSON · Markdown · 中文
75%Fix Rate
85%Confidence
1Evidence
2024-05-12First Seen

Version Compatibility

VersionStatusIntroducedDeprecatedNotes
ethtool 5.10-6.10 active — — —
Linux kernel 5.10-6.8 active — — —
Intel I350/i40e drivers 5.x-6.x active — — —
Broadcom bnxt_en driver active — — —
Mellanox mlx5 driver active — — —

Root Cause

The Ethernet interface failed to establish a link due to autonegotiation failure, typically caused by mismatched speed/duplex settings between the NIC and the switch port, or a faulty cable/connector.

generic

中文

以太网接口因自动协商失败而无法建立链路，通常由NIC和交换机端口之间的速度/双工设置不匹配，或电缆/连接器故障引起。

Official Documentation

https://www.kernel.org/doc/html/latest/networking/ethtool.html

Workarounds

  1. 80% success Check cable and connection: use `ethtool eth0` to see current settings, then test with a known-good cable. Replace if faulty. 
    Check cable and connection: use `ethtool eth0` to see current settings, then test with a known-good cable. Replace if faulty.
  2. 75% success Force both sides to the same speed/duplex: on Linux, `ethtool -s eth0 speed 1000 duplex full autoneg off` and configure the switch port to 1000/full. Verify with `ethtool eth0`. 
    Force both sides to the same speed/duplex: on Linux, `ethtool -s eth0 speed 1000 duplex full autoneg off` and configure the switch port to 1000/full. Verify with `ethtool eth0`.
  3. 70% success If autoneg is required, ensure both sides support the same capabilities: update NIC firmware or driver, and verify switch port configuration (e.g., `show interfaces status` on Cisco). 
    If autoneg is required, ensure both sides support the same capabilities: update NIC firmware or driver, and verify switch port configuration (e.g., `show interfaces status` on Cisco).

中文步骤

  1. Check cable and connection: use `ethtool eth0` to see current settings, then test with a known-good cable. Replace if faulty.
  2. Force both sides to the same speed/duplex: on Linux, `ethtool -s eth0 speed 1000 duplex full autoneg off` and configure the switch port to 1000/full. Verify with `ethtool eth0`.
  3. If autoneg is required, ensure both sides support the same capabilities: update NIC firmware or driver, and verify switch port configuration (e.g., `show interfaces status` on Cisco).

Dead Ends

Common approaches that don't work:

  1. Forcing speed/duplex on only one side (e.g., NIC set to 1000/full, switch set to auto) 85% fail

    Autonegotiation requires both sides to have matching settings; forcing one side while leaving the other on auto causes a duplex mismatch, leading to packet loss or no link.

  2. Replacing the NIC without testing the cable or switch port 60% fail

    The issue may be a bad cable or switch port; replacing the NIC wastes time and resources.

  3. Setting the interface to a lower speed (e.g., 100 Mbps) without verifying switch support 70% fail

    The switch port may not support 100 Mbps or may have a different configuration, causing the same failure.