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How to fix an IP address conflict

5 min read · Updated 2026-10-06

Two devices, one IP address: what causes an IP conflict, the exact steps to fix it on Windows, macOS and your router, and how to prevent it.

On this page

  1. What an IP conflict looks like
  2. The four usual causes
  3. Fix it step by step
  4. IPv6 conflicts
  5. Prevent the next one

An IP address conflict means two devices on the same network are using the same address. One of them will lose traffic unpredictably — pages half-load, the connection drops, or one device boots the other off the network. It is one of the oldest networking problems and still one of the easiest to fix.

What an IP conflict looks like

  • Windows: a notification or event log entry reading "Windows has detected an IP address conflict" or "Another device on the network is using your computer's IP address".
  • macOS/iOS: "Another device is using your computer's IP address" when joining a network.
  • Behaviour: intermittent connectivity on one device, slow or stuck transfers, Wi-Fi that connects but does not pass traffic, or a device that works until another joins the network.
  • Printers and IoT: an offline printer or camera that comes back when another device is switched off — a classic hidden conflict.

The four usual causes

  1. A static address inside the DHCP pool. Someone set a manual IP of 192.168.1.50 while the router is also free to hand .50 to a phone. Sooner or later, it does.
  2. Two devices configured with the same static address — often after a network device is replaced or re-configured from a backup.
  3. A second DHCP server. A rogue router, a repeater in router mode, or a misconfigured virtual machine (VMware, Hyper-V, VirtualBox all run virtual DHCP servers on host-only networks) starts handing out the same range.
  4. Lease-table confusion. Router reboots, firmware bugs or a device that keeps requesting an address it no longer holds — see why addresses change.

Fix it step by step

  1. Renew the lease. On the affected machine: Windows → ipconfig /release, then ipconfig /renew. macOS/Linux → toggle Wi-Fi or run sudo dhclient -r and sudo dhclient. This alone resolves most transient conflicts.
  2. Reboot the router to clear a stale or corrupted lease table, then let devices reconnect.
  3. Find the duplicate. On the router's client list, look for two entries with the same IP. On a desktop, arp -a shows the IP-to-MAC mapping on your segment — two different MACs claiming one address is the proof. A network scanner such as Fing or Advanced IP Scanner gives the same answer with a UI.
  4. Fix the manual device. If something has a static IP, move it outside the DHCP pool (for example the router reserves .100–.199, so give permanent devices .10–.99) or, better, convert it to a DHCP reservation keyed to its MAC — see MAC vs IP.
  5. Hunt rogue DHCP servers if the problem returns. Check whether a repeater, mesh node or second router is running its own DHCP, and switch it to bridge/AP mode.
  6. Update firmware on routers that repeatedly mis-handle leases.

IPv6 conflicts

IPv6 has its own duplicate detection: before using an address, a device sends a neighbour solicitation and backs off if someone answers. Conflicts here are rarer and usually come from two devices configured with the same static address, or a router advertising a prefix that clashes with another router on the same segment. The same fixes apply — let the router's autoconfiguration do its job and avoid manual v6 addresses inside the advertised /64, whose structure is explained in subnet masks and CIDR.

Prevent the next one

  • Let DHCP do the work. Use reservations instead of static configuration wherever the device supports it.
  • Keep a small map of your permanent addresses — router at .1, servers .2–.9, printers .10–.19, DHCP pool from .100. Conflicts become impossible by construction.
  • One DHCP server per network. Repeaters and mesh nodes belong in bridge mode.
  • Segment guest and lab devices with a VLAN or guest network so a misconfigured VM cannot collide with your home devices.

Bottom line: an IP conflict is two claimants for one address. Renew, reboot, then move the offender out of the DHCP pool — and prefer reservations over hand-typed addresses to make the problem structurally impossible. Your public IP is unaffected by any of this; conflicts live inside your LAN.

Frequently asked questions

What causes an IP address conflict?

Almost always two devices claiming the same address: a static IP inside the DHCP pool, duplicated manual settings, or a rogue DHCP server on a repeater or virtual machine.

Does restarting the router fix an IP conflict?

Usually yes for a transient conflict — it clears the lease table and forces new requests. If the conflict returns, one device has a static address or a rogue DHCP server is running, and a reboot is only a temporary mask.

Can two devices have the same IP address?

Physically yes, but only one can communicate reliably at a time. Both will see intermittent failures, and switches will flip their forwarding table between the two MAC addresses.

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