NIC link speed is changing between 100Mb/sec and 1000Mb/sec for no reason

Solution Verified - Updated -

Issue

  • Something is changing the ethernet network link speed to 100baseT/Full instead of 1Gb/sec.

  • ethtool shows the interface is no longer advertising 1000baseT/Full as an available link mode:

    $ ethtool eth0
    Settings for eth0:
        Supported ports: [ TP ]
        Supported link modes:   10baseT/Half 10baseT/Full 
                                100baseT/Half 100baseT/Full 
                                1000baseT/Full 
        Supported pause frame use: No
        Supports auto-negotiation: Yes
        Advertised link modes:  10baseT/Half 10baseT/Full 
                                100baseT/Half 100baseT/Full 
        Advertised pause frame use: No
        Advertised auto-negotiation: Yes
        Speed: 1000Mb/s
        Duplex: Full
        Port: Twisted Pair
        PHYAD: 1
        Transceiver: internal
        Auto-negotiation: on
        MDI-X: off (auto)
    Cannot get wake-on-lan settings: Operation not permitted
        Current message level: 0x00000007 (7)
                       drv probe link
        Link detected: yes
    

Environment

  • Red Hat Enterprise Linux 6
  • tuned service

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