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Random DHCP conflict


My customer has a DHCP server on his Cisco core switch C3560X. He is getting some recurrent DHCP conflict on his wired user DHCP pool. I have been asked to identify the cause of these DHCP conflicts. Could you help me investigating ? You will find my observations below and some show commands done on the switch attached.

I have checked the logs several times and here are my observations:

  • Gratuitous ARP DHCP conflict are always generated by a client following a down/up of the switchport on which the client is connected
  • The problem does not occure for the same client MAC-address nor the same port. It is always a different MAC and a different port of the switch
  • Sometimes, the problem occures every 2 or 1 hour

Do you have an idea of where does the DHCP conflicts comme from ? If you need some more information or show commands, do not hesitate to ask :)

Thank you for your help !


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