The short answer
Two devices holding the same address knock each other off intermittently. The usual cause is a manually set static address that sits inside the router’s automatic range. Move static addresses outside that range, or use DHCP reservations instead, and the problem disappears.
An IP conflict is easy to miss because it does not fail cleanly. Two devices work, then one stops, then the other, apparently at random. Printers, network drives and smart home devices are where people usually notice it.
How conflicts happen
- A static address inside the DHCP range. Someone gives a printer a fixed address that the router later hands to a phone. This is the most common cause by far.
- Two DHCP servers. A second router left in normal mode rather than access point mode hands out its own addresses, and the two pools overlap.
- A stale lease. A device returns from being switched off and reclaims an address already reassigned.
- A very small address pool in a house with many devices, causing rapid reuse.
Recognising one
- Windows shows a notification about an IP address conflict, which is unambiguous.
- A device works until another specific device is switched on.
- A printer or network drive appears and disappears intermittently.
- Two devices both report the same address in their network settings.
Fixing it
Find the DHCP range in your router
In the LAN or DHCP settings, note the start and end addresses — commonly something like 192.168.1.100 to 192.168.1.200. Everything inside that range belongs to the router to hand out.
Move static addresses outside the range
If you have manually configured devices, give them addresses below the range start — for example 192.168.1.10 to 192.168.1.50 — so the router can never allocate the same one.
Better still, use DHCP reservations
Instead of setting addresses on each device, tell the router to always give a specific device the same address. The device stays on automatic settings and the router guarantees consistency. This is more robust and much easier to see in one place.
Check for a second DHCP server
If you have a second router, it must be in access point or bridge mode with its DHCP server switched off. Two active DHCP servers on one network cause exactly this pattern and a great deal of confusion.
Release and renew on the affected devices
On Windows, run ipconfig /release then ipconfig /renew. On phones, forget and rejoin the network. On others, restart. This clears the duplicate immediately.
Enlarge the pool and lengthen the lease
If your address pool is small for the number of devices you own, enlarge it. Raising the lease time to 24 hours also reduces churn.
A note of which device has which address — even in a phone note — saves considerable time later. Most conflicts are created months after the fact by someone assigning an address that is already spoken for.
Frequently asked questions
What happens when two devices share an IP address?
Traffic for that address becomes ambiguous, so both devices suffer intermittent failures. Typically one works while the other is unreachable, and which one changes unpredictably.
Is a static IP better than a DHCP reservation?
A reservation is generally better. It achieves the same consistency while being managed centrally in the router, so the address cannot be allocated to anything else and you can see all of them in one list.
Can two routers cause IP conflicts?
Yes, if both are handing out addresses. The second should be in access point mode with DHCP disabled so only one device manages addressing.
How many addresses does a home network have?
A typical home range allows a couple of hundred, though the router’s default pool is often much smaller. Running out is a genuine problem in homes with many smart devices, and enlarging the pool is straightforward.
Look at your router’s DHCP range first. Nearly every conflict traces back to something manually configured inside it.
