Frequently Asked Question
Why does UniFi report a duplicate IP address or an unexpected DHCP server?
QUICK ANSWER
Look for conflicting static addresses or a second router handing out leases. An IP conflict and a rogue DHCP server are different faults, so identify which warning is present first.
Applies to: UniFi networks with intermittent access, changing gateways or duplicate-IP/DHCP warnings.
Work through these checks
- Capture the alert time, affected IP and device MAC addresses. Compare the client's gateway, DNS and DHCP server against the intended network settings.
- Review recent additions such as a spare router, travel router or restored gateway. A router connected by a LAN port may introduce an unintended DHCP service. Identify its owner before isolating it.
- For duplicate addresses, compare DHCP reservations with manually configured devices. Move static assignments outside the dynamic pool or create deliberate reservations, avoiding any address already in use.
- After correcting the conflict, renew the affected client's lease or reconnect it. If using DHCP guarding, configure the trusted server accurately and only on supported equipment; an incorrect rule can block legitimate leases.
Confirm the result
Check several affected clients after reconnection. They should keep unique addresses and the intended gateway, with no recurring warning during normal use.
If you need help
Include these details in your ticket: The warning screenshot, two relevant MAC addresses, DHCP scope/reservation details and recent network changes. Redact unrelated client information.
Updated 261107