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I have a Linux 2.6 box that uses ifplugd to bring up the network. While initialising, the logs say, "Initialisation complete. Link beat not detected." and then it goes into releasing the present address and obtaining lease all over again.

My question therefore would be:

  • What is link beat?
  • What does it mean if a link beat is not detected?
  • Why is this so critical? What determines if a link beat is present or not?
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Link beat is a signal generated by ports on ethernet hubs and switches; it allows your network card to detect/negotiate the speed of the connection and to verify that the connection is healthy. If the card cannot detect the beat, it assumes the connection is faulty and retries.

  • Test your cable to see if it is functioning (or try a new cable).
  • Try connecting a different box to the same switch using the same cable.

This may help you identify the point of failure.

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Still unclear about what causes "link beat"... Is thus some kind of crystal/oscillator in the network equipment? How is the beat detected? Is link beat a signalling protocol? – Arpith Oct 30 '12 at 13:14

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