What does `NO-CARRIER` and `DOWN` mean for a wireless interface?

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There is no document that would tell you what specially means for wireless. If your wifi is UP and NO-CARRIER means that is administratively up(ip link set dev wlan0 up) but not associated and authenticated with a SSID. Only LOWER_UP means that link layer is operational.

ip link list wlan0 and iw wlan0 link are 2 ways to retrieve link status information. The second form will show you if associated with a SSID, and show relevant wireless information.

Probably the cause of your link problems are related with Wireless power saving configurations, and thus the DORMANTstate of your interface.

Netlink interface flags:

IFF_DORMANT - Driver signals dormant

Check out the links below with instructions on how to chance this behavior.

Additional Documentation:

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adrian
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adrian

Updated on November 27, 2022

Comments

  • adrian
    adrian 12 months

    I have a remote server and I log output of certain commands while the server cannot access the internet.

    It uses a wireless interface to connect to the internet.

    In a working state the output of ip link list shows:

    3: wlan0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP mode DORMANT qlen 1000 link/ether 00:13:ef:b0:29:74 brd ff:ff:ff:ff:ff:ff
    

    When it is not working the output of ip link list shows:

    3: wlan0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc mq state DOWN mode DORMANT qlen 1000 link/ether 00:13:ef:b0:29:74 brd ff:ff:ff:ff:ff:ff
    

    What does this NO-CARRIER and DOWN mean for a wireless interface? In the case of ethernet, this would mean that the cable is disconnected.

    I would also appreciate any advice as to how I can further debug why the connection was not working. I also do a wicd-cli -y -l scan during the outage and it appears that the access point is still broadcasting. I cannot find any other hardware or software errors in the kernel messages.

    • Admin
      Admin almost 9 years
      It means the same thing as it does for a wired interface: you're disconnected.
    • Admin
      Admin almost 9 years
      @psusi Is there some documentation that tells that and could you share it please.
    • Admin
      Admin almost 9 years
      I wouldn't think you would need explicit instructions that the meaning you already established for that flag didn't change to something completely different just because you're using a wireless adapter.