Tutorials · Troubleshooting
How to Find and Fix an IP Address Conflict on Your Network
Two devices with the same IP address drop connections at random. Find both devices with ARP and the switch MAC table, then stop it from happening again.
Before you start
- Access to a computer on the same VLAN
- Read access to the switches (MAC address table) and the DHCP server
Step by step
Confirm the conflict
Windows and macOS often show an 'IP address conflict' warning. On Linux, arping in duplicate-detection mode reports any other device answering for the address.
sudo arping -D -I eth0 -c 3 10.1.10.25 # a reply means another device already uses 10.1.10.25
Find the MAC addresses
Ping the address and look at the ARP table. If the MAC address changes between checks, two devices are answering.
ping -c 2 10.1.10.25 && arp -n 10.1.10.25 # Linux/macOS ping 10.1.10.25 & arp -a 10.1.10.25 # Windows
Locate the switch port
Search the switch MAC address table for each MAC address. The port where it is learned, not an uplink, is where the device is connected.
Identify the device
The first half of the MAC address (OUI) shows the manufacturer. Together with the port location, this usually identifies the printer, camera or laptop.
Fix the address
Give the static device an address outside the DHCP pool, or convert it to a DHCP reservation.
Prevent it
Keep static addresses in a documented range, exclude that range from DHCP, and turn on DHCP snooping so only your DHCP server can hand out addresses.
Commands are generic, industry-standard examples. Exact syntax and menu names vary by model and firmware; check your device's manual on the Documentation page.
Pro tips
- Keep an IP address plan (spreadsheet or IPAM tool) with every static address.
- Cameras and printers shipped with the same default IP cause conflicts when installed together: change them one by one.
FAQ
Frequently asked questions
Can DHCP cause a conflict?
Yes, if two DHCP servers hand out the same range, or a device has a static IP inside the DHCP pool.
Keep learning
Related guides
Plan IP addressing and subnets
Read more →DHCP scopes and reservations
Read more →Stop rogue DHCP and ARP spoofing
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Read more →Stuck on a step?
Ask Navijin technical support or an authorised partner for help with your configuration.