How to Fix IP Address Conflicts on Your Local Network

“Windows has detected an IP address conflict.” If you've seen that message — or a device that simply refuses to connect — two machines are fighting over the same address. Here's exactly why it happens and how to fix it for good.

What an IP conflict actually is

Every device on a network needs a unique IP address, just like every house on a street needs a unique number. An IP address conflict happens when two devices end up assigned the same address. The network can't tell them apart, so traffic gets misdelivered and one or both devices lose connectivity — often intermittently, which makes it maddening to diagnose.

The common causes

• Two static IPs the same. Someone manually set the same address on two devices.
• Static IP inside the DHCP range. A device has a fixed address that the router's DHCP server later hands to another device automatically.
• Two DHCP servers. A second router or a misconfigured access point is also handing out addresses.
• Stale DHCP leases. A device returns from sleep and reclaims an address that was reassigned while it was away.
• Router glitches. Cheap or overloaded routers occasionally double-assign after a reboot.

Step 1: Confirm it's really a conflict

The telltale signs are an explicit “IP address conflict” warning, a device that connects then drops every few minutes, or an address that shows as 169.254.x.x (APIPA) — a sign the device failed to get a valid lease. You can confirm which addresses are in use with a quick command:

• Windows: ipconfig /all then arp -a to list addresses on the network.
• macOS/Linux: ifconfig or ip addr, plus arp -a.

Step 2: The 60-second fix (renew the lease)

For a one-off conflict, forcing the device to request a fresh address resolves it immediately:

• Windows: open Command Prompt and run ipconfig /release then ipconfig /renew.
• macOS: System Settings → Network → your connection → Details → TCP/IP → Renew DHCP Lease.
• Linux: sudo dhclient -r && sudo dhclient.
• Any device: simply toggle Wi-Fi off and on, or reboot. The router usually assigns a different free address.

Step 3: Fix the root cause

Reserve addresses instead of setting them statically

The single best long-term fix is a DHCP reservation. Rather than hard-coding an IP on the device (which the router doesn't know about), you tell the router to always give a specific device the same address based on its MAC. The router now owns the mapping, so it will never hand that address to anyone else. Look for “Address Reservation,” “DHCP Reservation” or “Static Lease” in your router admin panel, identify the device by its MAC address, and assign it an address.

Keep static IPs outside the DHCP pool

If you must use manual static IPs (for a server or printer), make sure they fall outside the router's DHCP range. For example, if DHCP hands out 192.168.1.100–192.168.1.200, assign static devices something like 192.168.1.10. Use the subnet calculator to confirm the addresses are valid for your network.

Hunt down a rogue DHCP server

If conflicts persist, a second device may be handing out addresses. The usual culprit is a second router that should be in “access point” or “bridge” mode but still has DHCP enabled. Log into each router and ensure only one device has a DHCP server running.

Step 4: Prevent it from coming back

• Reserve addresses for everything that matters: NAS, printers, servers, smart-home hubs.
• Keep router firmware updated — DHCP bugs are a common fix in updates.
• Widen the DHCP pool if you have many devices, so the router never runs short.
• Reboot the router after major network changes to clear stale leases.

Rule of thumb: let the router manage addresses through reservations. The moment you have two places deciding who gets which IP, conflicts become inevitable.