IP conflict checker — find the device causing an IP address conflict
A browser can't scan your LAN, but your computer already knows who is on it. Run one command, paste the output below, and this tool finds duplicate IP addresses, flags suspicious ARP entries and identifies each device's manufacturer by its MAC address. Nothing is uploaded.
arp -aarp -anip neigh or sudo arp-scan -l
All devices found
| IP address | MAC address | Vendor | Interface | Status |
|---|
How this finds an IP conflict
Every device keeps an ARP table — a cache that maps IP addresses on the local network to the hardware (MAC) address that answered for them. When two devices claim the same IP, the cache records both MAC addresses for that IP over time, or flips between them. That's the fingerprint of an IP address conflict, and it's exactly what this checker looks for.
- Same IP, different MACs — a real conflict: two devices are using that address. The vendor column tells you which two (e.g. a printer and a phone).
- One MAC answering for many IPs — normal for a router with several addresses, but if your gateway's MAC also appears against other devices' IPs it can indicate ARP spoofing or proxy ARP.
- 169.254.x.x addresses — a device failed to get a DHCP lease, often because it detected a conflict and gave up.
Test whether a specific IP is already taken
Before you assign a static address, check nothing answers on it:
- Windows:
ping -n 2 192.168.1.50thenarp -a | findstr 192.168.1.50. If an entry appears, the address is in use. - macOS:
ping -c 2 192.168.1.50; arp -n 192.168.1.50 - Linux:
sudo arping -D -I eth0 -c 3 192.168.1.50— Duplicate Address Detection; any reply means another device owns it.
Ping alone isn't proof — many devices block ping — but they can't hide from ARP, which is why the ARP check is the reliable one.
Found the conflict — now what?
Give one of the two devices a different address, then stop it recurring with a DHCP reservation on the router. Our step-by-step guides cover both: how to fix IP address conflicts and how to find which device is causing an IP conflict. If the conflict is between two whole networks (home router vs office VPN, or two routers), see fixing subnet overlap.
Frequently Asked Questions
How do I check for an IP conflict on my network?
Run arp -a (Windows/macOS) or ip neigh (Linux) and look for the same IP listed with two different MAC addresses — or paste the output into this checker to do it automatically. Your router's DHCP client list is another good source.
What command shows which MAC address is mapped to an IP address?
arp -a on Windows and macOS, or ip neigh show on Linux. Ping the IP first so it's in the cache, then filter: arp -a 192.168.1.56.
Can a browser-based tool scan my network for conflicts?
No. Browsers deliberately block access to ARP and local network scanning for security. That's why this tool analyses output you paste from your own machine — it never leaves your browser.
Will a device with an IP conflict always be disconnected?
Not necessarily. Often both devices work intermittently as the network's ARP caches flip between them, which is why conflicts show up as random drop-outs rather than a clean failure. Windows and macOS usually show a warning; many IoT devices fail silently.
What is the difference between an IP conflict and a MAC conflict?
An IP conflict is two devices using the same IP address. A MAC conflict (the same MAC on two devices) is much rarer — usually cloned virtual machines or spoofed adapters. This tool reports both.
Know the MAC, need the maker?
Paste any MAC address or OUI prefix — in any format — to find the manufacturer.
Open MAC Address Lookup