IP, routing and IPv6

IP address conflict on a Mac

Two devices on one network cannot use the same IP address. macOS checks for a conflict before it uses an address.

Applies to: macOS 13 Ventura and later for the System Settings steps. The Terminal commands work on all current macOS versions.Checked: 29 October 2026

Symptoms

macOS shows a message that another device uses your IP address.
The connection stops and starts again.
The problem starts after a new device joins the network.

Likely causes

A manual address that DHCP also gives. A device with a fixed address inside the DHCP range can take an address that the router gives to the Mac.
Two devices with the same manual address. Someone typed the same address on two devices.
Two DHCP servers. A second router or a hotspot on the same network gives out addresses from the same range.

How to check

Show the service's address and settings.
```
networksetup -getinfo Wi-Fi
```
List the devices that the Mac has talked to on the local network.
```
arp -a
```
Show which DHCP server gave the address. Look at the server_identifier line.
```
ipconfig getpacket en0
```

How to fix it

If the Mac uses DHCP, wait a few minutes. Apple says the DHCP server usually gives the Mac another address.
Renew the lease to get a new address now. See Renew the DHCP lease on a Mac.
If you typed the address by hand, make sure that it is correct and not in the router's DHCP range.
On a managed network, ask the administrator for a free address.
Remove or turn off a second DHCP server, such as an extra router in router mode.

With Kilobat

The CLI lists devices from the Mac's neighbor cache, with names that you gave them.
```
kilobat devices
```

Questions

Can the router reserve an address for my Mac?

Many routers can. Look for DHCP reservation in the router's settings.

Sources

Apple Support: Resolve IP address conflicts on Mac
ipconfig(8), man page installed with macOS 27.2
arp(8), man page installed with macOS 27.2
Apple Support: Change TCP/IP settings on Mac

Sources checked on 29 October 2026. Man pages are the ones installed with macOS; open one with man <name> in Terminal.