You are working along and a notification slides down: "Another device on the network is using your computer's IP address." Web pages stall, downloads die mid-stream, and the connection feels like it comes and goes for no reason. Nothing is broken — two devices on your Wi-Fi simply grabbed the same IP address, and the router does not know which one to talk to. This is an address collision, and it clears in a couple of minutes once you know the order to work through.
The fixes, fastest first
Do these in order. Most people are fixed by step 2.
1. Renew the DHCP lease (30 seconds)
This forces the router to hand your Mac a fresh, unused address — it resolves the collision directly. Open System Settings → Wi-Fi → Details… (next to your network) → TCP/IP and click Renew DHCP Lease. On older macOS it lives in System Preferences → Network → Advanced → TCP/IP. Give it five seconds and try a page.
2. Toggle Wi-Fi off and on
The simplest reset. Click the Wi-Fi icon in the menu bar, turn Wi-Fi off, wait ten seconds, and turn it back on. Your Mac re-requests an address from scratch. If you are on Ethernet, unplug the cable for ten seconds and plug it back in.
3. Restart the router — and give it two full minutes
The collision usually starts at the router, not the Mac. Its DHCP table (the list of which device owns which address) can get stale, especially after a lot of devices join and leave. Unplug the router, wait two full minutes so the table clears, then power it back on. This is the single most reliable fix when the alert keeps returning for everyone in the house, not just you.
4. Reboot the other device (or take it off the network)
The error names another device for a reason — a phone, a smart TV, a printer, or an old laptop is holding the address your Mac wants. Rebooting that device, or turning its Wi-Fi off for a moment, lets the router reassign cleanly. A cheap Wi-Fi plug or IoT gadget with a hard-coded static IP is a common repeat offender.
5. Set a manual IP as a test
If it keeps happening, pin your Mac to an address outside the router's automatic pool. In Wi-Fi → Details… → TCP/IP, set Configure IPv4 to Manually and choose an address high in your range (for example 192.168.1.240 if your router is 192.168.1.1). This sidesteps the DHCP scramble entirely. If it fixes things, switch back to Using DHCP afterward, or leave it manual — either is fine.
6. Reserve the address in your router (the permanent fix)
The lasting cure is a DHCP reservation: log into your router (usually 192.168.1.1 in a browser), find the DHCP or LAN settings, and tie your Mac's Wi-Fi MAC address to one dedicated IP. After that no other device can ever be handed it. Find your Mac's address under Wi-Fi → Details… → Hardware (the Wi-Fi Address / MAC).
7. Delete the network configuration files
If a corrupted config is stuck handing you a bad address, clear it. In Finder press Command-Shift-G, go to /Library/Preferences/SystemConfiguration/, and move these to the Trash: com.apple.airport.preferences.plist, NetworkInterfaces.plist, and preferences.plist. Restart — macOS rebuilds them clean and re-requests an address.
Why this is different from a "self-assigned IP" error
They look similar but are not the same. An IP conflict means your Mac did get an address — another device just also has it. A self-assigned IP address (169.254.x.x) means DHCP failed entirely and your Mac gave up and invented one, so it has no working address at all. If you see a 169.254 number, follow the self-assigned guide instead. If the trouble is intermittent — fine, then drops, then fine — it may be a flakier radio issue covered in Wi-Fi keeps dropping. And if pages resolve slowly rather than not at all, it is often DNS — see how to change DNS on a Mac.
When it is the hardware, not the network
An IP conflict is almost never a hardware fault — it is a router/address problem, and every fix above is free. But if your Wi-Fi is also genuinely unreliable (drops on wake, weak signal in every room, the card disappears from System Settings), the Wi-Fi module or logic board may be failing, and that is a different problem. A board-level Wi-Fi repair often runs $400–$600, which on an older Mac is more than the machine is worth. In that case it is usually smarter to trade it in — we buy Macs with broken Wi-Fi and put the credit toward one that just works. Our refurbished machines start at $569.99 on the Apple clearance page, each with a one-year warranty and free shipping.
Frequently Asked Questions
What does "another device is using your IP address" actually mean on a Mac?
Two devices on the same network were assigned the same local IP address by the router. Your Mac detected the duplicate and warned you because it cannot reliably send and receive data while another device answers to the same address. Renewing the DHCP lease (fix 1) resolves it in seconds.
Will an IP conflict fix itself?
Sometimes — the router may reassign addresses on its own within a few minutes. But it tends to come back, because the underlying cause (a crowded or stale DHCP pool, or a device with a hard-coded static IP) is still there. A router restart plus a DHCP reservation for your Mac (fixes 3 and 6) stops it for good.
Is this a Mac problem or a router problem?
Usually the router. If several devices in your home see the warning, restart the router. If only your Mac does, renew its lease or set a manual IP. It is almost never a fault with the Mac itself.
Can two devices really share one IP address?
They should not, but it happens when a device is given a static IP that overlaps the router's automatic DHCP range, or when the router's lease table gets confused after many devices connect and disconnect. Reserving each device's address in the router prevents the overlap.