IP Address Conflicts: Why Windows Says "Another Device Is Using This Address", the Internet Drops and the Printer Goes Missing

Every device on a network — computer, phone, printer, camera — needs its own unique IP address, like a flat number in a building. If two devices get the same address, confusion follows: data goes to the wrong place, the internet drops first on one device and then another, the printer "goes missing", and Windows reports that an IP address conflict has been detected on the network. Let's look at where these conflicts come from, how to find them and how to get your network in order.

How devices get their addresses

On a home or office network, addresses are usually handed out by the router using a service called DHCP: a device connects, asks for an address and receives a free one from a set range, for example 192.168.1.100 to 192.168.1.200. The router remembers which address went to whom, so in normal operation there are no conflicts. Problems start when a second address-giver appears on the network, or when someone's address has been set manually.

The main causes of conflicts

• Two DHCP servers on the network. The most common cause. For example, your own router was connected to the provider's router through a LAN port rather than the WAN port, and both hand out addresses. Or a second router is used as an access point but its DHCP hasn't been turned off.
• A static address inside the DHCP range. A printer, camera or computer was manually given an address such as 192.168.1.120, and the router gave the same address to a phone.
• A device moved from another network. A printer or camera with a fixed address from an old office.
• A router fault. A frozen router, or a range of addresses that's too small for a large number of devices.
• Repeaters and mesh in the wrong mode — for example, a second unit working as a separate router.

The signs

• A Windows message about an IP address conflict.
• The internet drops on one device when another is switched on.
• The network printer sometimes prints and sometimes isn't reachable.
• CCTV cameras periodically disappear from the recorder.
• Devices get addresses from different ranges, such as 192.168.0.x and 192.168.1.x, and can't see each other.
• Double NAT: games and video calls complain of a strict connection type.

How to connect a second router properly

If you have both the provider's router and your own, choose one of these setups:

• The provider's router in bridge mode, with your router connected to it through the WAN port and handing out addresses to the whole network. The cleanest option.
• Your router in access point mode: connected to the provider's router through a LAN port, with its DHCP turned off, so only the provider's router hands out addresses.

A mixed setup — where both hand out addresses on one network — is what causes most conflicts.

Static addresses done properly

It's handy for printers, cameras, NAS units and recorders to have a permanent address so computers don't "lose" them. The right way is not to set the address manually on the device but to reserve it in the router (a DHCP reservation by MAC address). If an address is set manually after all, it must be outside the range the router hands out, and recorded in a list of the network's addresses.

How to find the culprit

First check which router is handing out addresses and whether there's a second DHCP server: the gateway address on a computer shows where it got its settings from. Then look at the client list in the router and find devices with fixed addresses. Temporarily switching devices off one by one also helps: the conflict disappears when the "extra" one is off. In an office it's worth keeping a simple table of which device has which address.

A temporary fix

If a conflict appears suddenly, restarting the router and the device often helps for a while: addresses are handed out afresh. But if the cause is two DHCP servers or a static address, the problem will come back. That's why it's important to find and fix the root cause.

What our technician does

1. Checks the network layout: which routers, access points and switches are connected, and how.
2. Finds extra DHCP servers and devices with static addresses.
3. Puts routers into the right modes: bridge, access point, one unified network.
4. Reserves addresses for printers, cameras and NAS units in the router and draws up an address table.
5. Checks that every device works and that there's no double NAT.

A real example

In a small office on Guramishvili Avenue, the network printer became unreachable several times a day, and two employees periodically lost internet access with an address conflict message. Our technician found that a second router for Wi-Fi was connected to the provider's router through a LAN port, and both were handing out addresses. On top of that, the printer had once been manually given an address from the middle of the DHCP range. We switched the second router to access point mode, reserved the printer's address in the router outside the handed-out range and reinstalled the printer on the computers. The printer stopped going missing, and the conflict messages disappeared.

Call a technician

If your network has an IP address conflict, the internet keeps dropping or devices go missing, we'll come to any district of Tbilisi around the clock. Learn more on our network troubleshooting, local network setup and router setup pages.