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I have a case of clients on my LAN losing its MAC address. This seems to happen randomly to clients even though they had both an IP address and MAC addresses (when "arp") during the initial boot up.

After the MAC address is lost (incomplete), I am unable to ping or ssh to that client; nor does a reboot work.

Anyone have ideas?

Description of LAN (closed system, not connected to the internet). - ~100 clients all set to static IP address through /etc/network/interfaces - ~1 core switch - ~16 access switches (daisy chained) - Linksys router

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MAC address can not be lost. MAC address is hardware address on nic. If you got incomplete that means that no network connection with IP address. I have same problem when network cable was damaged. Maybe is port on switch in problem.

  • Current mac address you can see with command ifconfig on host – 2707974 Mar 4 '14 at 12:45
  • This... was exactly my problem. I bumped a cable earlier in the day and was having this behavior with arp -a, and after wiggling the cable again, everything worked like new. Time for a new cable! – geerlingguy Jul 3 '16 at 4:35
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I suspect a damaged switch or loose cables/connection. Check your cables, connections, the switches.

Here is an example I recently observed of how this can happen using wireless clients that loose connection:

  1. An android phone connects to the network. The router/dhcp server caches its name and IP address, something like this: android-1234567890 192.168.1.125
  2. The phone goes to sleep, looses connection.
  3. A service on a PC tries to connect the phone (e.g. pings). The ARP request is sent, but there is no response from the sleeping phone with the MAC address. But the record is stored anyway.

    $ ping 192.168.1.125

  4. The user asks ARP for all or the specific IP address, but gets the incomplete MAC:

    $ arp 192.168.1.125

    android-1234567890 (192.168.1.125) at <incomplete> on eth0

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I think it is very unlikely that a MAC address is lost or incomplete. In the case of my home PC i somehow managed to overwrite the MAC persistently to 12:34:56:78:90:ab . So i have a problem now with wake on lan. In your case it seems that the problem can persist a reboot but not a shutdown/startup of a single pc. Have you checked if unplugging/replugging the network cable changes something?

What Kernel-Version are you using? Is there maybe a problem with your switch setup? I had problems with Flow-Control in the past.

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The behavior you describe sounds a lot like what can happen if two systems are set to the same IP statically.

Description of LAN (closed system, not connected to the internet). - ~100 clients all set to static IP address through /etc/network/interfaces - ~1 core switch - ~16 access switches (daisy chained) - Linksys router

You should double check and make sure none have a duplicate address, and also that the netmasks are all correct.

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