Duplicate IP Addresses and Rogue DHCP Servers

A duplicate IP address can cause disruptions in network connectivity. UniFi provides a system log to notify you if this ever occurs so that you can promptly address it. The two main causes for this issue are:

  • Statically setting IP addresses on the device(s)
  • A Rogue DHCP server on the network

Static IP Addresses

Duplicate IP addresses can result if you set a static IP directly on the NIC of a device, without removing it from your DHCP Range. To fix this:

  1. Select the Network with an overlapping IP address and navigate to its DHCP Range.
  2. Take note of the Start and Stop values.
  3. Change the range or change the static IP to ensure that the IP address is outside of the range.
  4. You may need to reboot the client to take effect.

Check for a Rogue DHCP Server

If there are no static IPs configured but still experience duplicate IP addresses, then you likely have a rogue DHCP server on the network. If you are unable to find the rogue DHCP server to remove or disable it, then we recommend enabling DHCP Guarding. To do so:

  1. Select a Network.
  2. Enable DHCP Guarding.
  3. Enter the IP address of your trusted DHCP server. If you have a UniFi gateway and are using the built-in server, use the network's Gateway IP here.
  4. DHCP offers will be blocked from all but the specified DHCP server.

Note: DHCP guarding requires UniFi switches.

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