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Kerio Control DHCP server is assigning the same IP address to two different MAC addresses

Author: Nico Suprajitno Updated

Overview

  • A certain MAC address is given an IP address already assigned to another by the DHCP server.
  • Searching for that MAC address yields several devices.
    mceclip0.png
  • Debug log shows multiple DHCPDISCOVER messages received even though the DHCPOFFER was sent previously. 
    [12/Oct/2021 07:28:17] {dhcp} DHCP server [Transaction ID 0x7D983498]: sending DHCPOFFER to 5a-ef-68-00-4f-58 (dest ip = 255.255.255.255, offered address = 10.0.0.238)
    [12/Oct/2021 07:28:22] {dhcp} DHCP server [Transaction ID 0x7D983498]: received DHCPDISCOVER from 5a-ef-68-00-4f-58 (source ip = 0.0.0.0)
    [12/Oct/2021 07:28:22] {dhcp} DHCP server [Transaction ID 0x7D983498]: sending DHCPOFFER to 5a-ef-68-00-4f-58 (dest ip = 255.255.255.255, offered address = 10.0.0.238)
    [12/Oct/2021 07:28:30] {dhcp} DHCP server [Transaction ID 0x7D983498]: received DHCPDISCOVER from 5a-ef-68-00-4f-58 (source ip = 0.0.0.0)
  • Host log shows a few different MAC addresses changed to the MAC address in question. The devices whose MAC addresses changed are Android devices.mceclip1.png

Solution

Android devices seem to be switching MAC Addresses frequently, resulting in the observed behavior. To resolve this, advise the users with android devices to change their Wi-fi settings to use the device MAC instead of randomized MAC.

Note: By default, Android 10 and onwards have randomized MAC settings enabled.

 

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