Windows shows Windows has detected an IP address conflict when two devices on the same network share the same IPv4 address. The fastest fix is to open an administrator Command Prompt and run ipconfig /release then ipconfig /renew, then restart your router. If the error returns, a device on your network has a static IP set inside the router's DHCP assignment range — finding and changing that address is the only permanent fix.

What the error actually means

Every device on a local network needs a unique IPv4 address to send and receive traffic. Windows detects the conflict using ARP (Address Resolution Protocol): after claiming an address via DHCP, your machine broadcasts a message asking whether any other device owns that IP. If another device replies with a different MAC address, Windows raises the conflict notification. Your adapter may lose connectivity immediately or flap between working and broken until one device backs off and releases the address.

The conflict lives entirely on your local network. Your public IP from the ISP is unrelated, and neither changing DNS servers nor rebooting only the modem will resolve it.

Root causes, ranked by frequency

1. Static IP set inside the DHCP pool

A printer, NAS, IP camera, smart TV, or another computer was given a fixed IP address directly on the device. That address falls inside the range the router hands out automatically via DHCP. When the router later assigns that same address to a newly connected device, the conflict fires. This is the cause in the large majority of home and small-office cases.

2. Stale or duplicate DHCP lease

A device reconnects before its previous lease has fully expired, or the router's lease table gets corrupted after a power cut or firmware update. The router re-issues the same IP to a second device before clearing the old entry. A full router restart — power unplugged for 30 seconds, not just a Web UI reboot — flushes the lease table and forces every device to request a fresh assignment.

3. Duplicate static addresses on two devices

Two devices were each manually assigned the same IP, usually during initial setup or after copying network settings from one machine to another. Neither device is misconfigured in isolation — the conflict arises because no one checked for overlap. This is more common in small offices after a network reconfiguration than in home settings.

4. A rogue or second DHCP server

A second router, a misconfigured access point left in router mode, or a virtual machine running its own DHCP service is handing out addresses from a pool that overlaps with the primary router's pool. Connecting a second router with DHCP still enabled on both devices is the most common way this appears in home networks.

Quick fix: release and renew your DHCP lease

Open Command Prompt as administrator — on Windows 10 and 11, right-click Start and choose Terminal (Admin) or Command Prompt (Admin). Run these three commands in sequence:

ipconfig /release ipconfig /flushdns ipconfig /renew

After /renew completes, read the output. A healthy result shows an IPv4 address in one of the private ranges: 10.x.x.x, 172.16.x.x through 172.31.x.x, or 192.168.x.x. If the address starts with 169.254, the adapter self-assigned an APIPA address, which means DHCP failed entirely — the router may be unreachable, the DHCP pool may be exhausted, or DHCP has been disabled on the router.

After the renew, unplug the router for 30 seconds. This flushes its lease table and forces every device on the network to request a fresh address assignment, clearing stale-lease conflicts at the source.

Finding the conflicting device with arp -a

If the error reappears after a renew, identify the other device before making further changes. In the same administrator Command Prompt, run:

arp -a

This displays every IP-to-MAC address mapping your machine has cached. Find the IP address named in the Windows conflict notification — it is also visible in ipconfig /all under your active adapter. If the ARP entry for that IP shows a MAC address that does not match your own adapter's Physical Address (also listed in ipconfig /all), the listed MAC belongs to the conflicting device.

To identify the device, log into your router's admin panel and open its connected-device or DHCP-client list. First find your router's admin address: run ipconfig /all and read the Default Gateway value on your active adapter. Type that address into a browser. Common values include 192.168.0.1, 192.168.1.1, 10.0.0.1, and 192.168.2.1, but always use the value shown in your own output — do not assume. In the admin panel, look for a section labelled DHCP Client List, Connected Devices, or LAN Hosts (names vary by firmware and brand) and match the MAC address to a hostname or device type.

Reading Windows Event Viewer for conflict history

Windows logs every IP conflict in the System event log. Press Windows + R, type eventvwr.msc, press Enter, and navigate to Windows Logs → System. Filter by Event ID 4198 (IPv4 conflict detected) or 4199 (address already in use by another device). Each entry records the exact time, the conflicting IP address, and the MAC address of the device that responded to the ARP probe.

This is useful when the conflict happened earlier in the day and you missed the notification. It also serves as confirmation after a fix: if no new 4198 or 4199 entries appear over the following 24 hours, the conflict is resolved. DHCP leases typically last 24 hours, so a static-IP conflict may not re-fire until the next renewal cycle if you only ran /renew without correcting the underlying static address.

Tip: after reviewing Event Viewer, cross-reference the conflict timestamp with your router's DHCP log (often under Advanced → System Log or a similar path, though this varies widely by firmware) to identify which device was handed the address at that moment. Not all consumer routers retain DHCP logs, but those that do make root-cause identification much faster.

Switching from a static IP to automatic on Windows

If your Windows machine itself has a manually configured static IP that falls inside the router's DHCP pool, removing that static assignment fixes the conflict directly.

  1. Press Windows + R, type ncpa.cpl, press Enter to open Network Connections.
  2. Right-click your active adapter (Ethernet or Wi-Fi) and choose Properties.
  3. Select Internet Protocol Version 4 (TCP/IPv4), then click Properties.
  4. Choose Obtain an IP address automatically and Obtain DNS server address automatically.
  5. Click OK and close all dialogs.

On Windows 11, reach the same setting via Settings → Network & Internet → your adapter name → Edit next to IP assignment → Automatic (DHCP). The adapter requests a new lease immediately. Confirm with ipconfig /all: DHCP Enabled should read Yes and the IP should be in a valid private range.

Using a DHCP reservation instead of a static IP

For devices that need a consistent address — printers, NAS boxes, IP cameras — the correct method is a DHCP reservation configured on the router, not a static IP set on the device itself. A reservation instructs the router to always issue the same IP to a specific MAC address while still running the normal DHCP process. The device stays set to automatic, the address is excluded from the dynamic pool, and conflicts cannot arise.

To add a reservation, log into the router admin panel via your default gateway address. Find a section labelled Address Reservation, Static DHCP, or DHCP Reservation — terminology varies by firmware version and brand. Enter the device's MAC address (from ipconfig /all, or printed on a label on the hardware) and the IP you want it to always receive. Save and apply. The device should release its current lease and renew to pick up the reserved address.

For the authoritative protocol-level specification of how DHCP lease assignment and reservations are meant to work, see RFC 2131: Dynamic Host Configuration Protocol.

Tip: document every static IP and DHCP reservation in a plain text file alongside your router admin credentials — a simple table of hostname, MAC address, and assigned IP prevents future conflicts when a new device is added. The DNS Lookup tool can confirm that any internal hostnames continue to resolve correctly after you change address assignments.

Adjusting the DHCP pool to exclude static addresses

If you have devices with static IPs you cannot change, shrink the router's DHCP pool so it never hands out those addresses. In the router's DHCP server settings, set the pool start address above the highest static IP in use. If static devices occupy addresses ending in .2 through .20, set the DHCP pool start to .21. The end address controls how many devices can be served dynamically.

This approach requires updating the pool boundaries whenever a new static device is added. The DHCP reservation method above is cleaner for most environments because the router tracks the exclusions automatically and device settings remain on automatic.

Dealing with a rogue DHCP server

If the conflict error appears on multiple machines simultaneously, or devices receive addresses outside the expected subnet, a second DHCP server is competing with your router. Common sources:

  • A second router connected LAN-to-LAN with its own DHCP server still active. Log into the second router and disable its DHCP server. Only the primary router should serve DHCP on the LAN.
  • A virtual machine using a bridged or internal adapter with its own DHCP service. Disable the VM's DHCP service or switch its network mode to NAT.
  • A wireless access point left in router mode instead of AP mode. Check whether the device has a hardware or software switch for access-point mode and enable it.

To detect a rogue DHCP server, install Wireshark and capture on the active adapter using the display filter bootp.type == 2 (DHCP Offer frames). If offers arrive from a source IP other than your primary router, that source is the rogue server. On managed switches, enabling DHCP Snooping restricts DHCP offer traffic to designated trusted ports, blocking rogue servers from reaching clients.

Verifying the fix worked

Run these commands after applying any fix and check each result:

ipconfig /all arp -a ping <your_default_gateway>
  1. ipconfig /all: DHCP Enabled reads Yes, the IPv4 address is in a valid private range, and Lease Obtained shows a recent timestamp.
  2. arp -a: the previously conflicting IP appears only once, with a MAC that matches your own adapter's Physical Address from ipconfig /all.
  3. Ping your gateway: substitute the Default Gateway value from ipconfig /all. Four replies with 0% packet loss confirm layer-3 connectivity is restored.

Monitor Event Viewer (eventvwr.msc → Windows Logs → System) over the following 24 hours. Absence of Event ID 4198 and 4199 entries confirms the conflict has not recurred. To also verify that external DNS resolution is working after restoring connectivity, the DNS Propagation Checker shows whether your domain resolves correctly from 12 public resolvers.

Other operating systems

macOS

macOS detects conflicts silently — a brief connectivity drop or a System Settings notification is usually the only signal. To renew a DHCP lease: System Settings → Network → Wi-Fi → Details → TCP/IP → Renew DHCP Lease. From Terminal: sudo ipconfig set en0 DHCP, substituting the actual interface name shown by ifconfig. Find the default gateway with netstat -nr | grep default or route -n get default.

Linux

On systemd-based distributions (Ubuntu 20.04+, Debian 11+), reapply settings with NetworkManager: nmcli device reapply eth0. Or use dhclient to release and renew:

sudo dhclient -r eth0 sudo dhclient eth0

Check for ARP conflicts before claiming an address: arping -D -I eth0 <suspect_IP> — any reply means the address is already in use. View the current routing table: ip route show. Inspect NetworkManager DHCP events with journalctl -u NetworkManager | grep DHCP.

iOS and Android

Neither platform labels the conflict explicitly — you see No Internet Connection or a warning triangle on the Wi-Fi icon. On iOS: Settings → Wi-Fi → tap the network name → Configure IP → set to Automatic if it was on Manual. On Android: long-press the network name → Modify network → Advanced options → IP settings → DHCP. Neither OS exposes arp or ipconfig equivalents; use a network scanner app to enumerate all devices and spot duplicate IPs across the LAN.

Common misdiagnoses

  • Blaming the ISP. The conflict is LAN-local. Your public IP, the modem, and the ISP's infrastructure are not involved and cannot fix it.
  • Blaming the VPN. A VPN creates a separate virtual adapter with its own IP assignment. A conflict on the physical adapter is independent. That said, a VPN client that runs its own DHCP service can create conflicts on the virtual interface — check all adapters in ipconfig /all.
  • Replacing the router. If the device with the conflicting static IP reconnects to the new router, the same conflict fires again. Identify and fix the static IP assignment first.
  • Ignoring a self-resolving error. Windows sometimes recovers automatically after one device backs off. The root cause remains and the conflict will return. A five-minute fix now costs far less than a dropped video call or a failed backup later.

IPv6, DoH, and DNSSEC in 2026

IPv6 builds Duplicate Address Detection (DAD) into the protocol itself. Before claiming an address, a device sends a Neighbor Solicitation and waits to see whether anything replies. Genuine IPv6 conflicts are uncommon in practice unless DAD has been explicitly disabled. When they occur, Windows logs them as Event ID 4300 (link-local address conflict) or 4320 (global unicast address conflict) in the System event log under source Tcpip.

DNS over HTTPS (DoH) and DNS over TLS (DoT) — increasingly the default in Windows 11 and major browsers as of 2026 — encrypt DNS queries in transit but operate entirely above the IP layer. They have no relationship to DHCP address assignment or conflict resolution. An IP conflict disrupts all IP traffic regardless of which DNS transport is in use. If a browser shows a DNS resolution failure alongside an IP conflict notification, fix the IP conflict first — DNS resolution recovers once routing is restored.

DNSSEC validates cryptographic signatures on DNS records and similarly operates above the IP layer. A DNSSEC validation failure appearing at the same time as a conflict error is a symptom of broken routing, not of invalid DNS records. Restore the IP assignment first, then recheck DNSSEC status once full connectivity is confirmed.