Every time a phone joins your Wi‑Fi, it gets an address, a route to the internet, and a way to look up website names, without you typing anything. The service doing that is DHCP. You only notice it when it breaks: Windows saying it "doesn't have a valid IP configuration," a "Self-Assigned IP" warning, or an IP conflict message.
This guide covers what DHCP does inside a normal home network, what your router hands out, and how to fix the common errors. It is about the local side of your network. If you want to know why your public IP changes over time, read Does Your IP Address Stay the Same? instead.
Short answer
DHCP (Dynamic Host Configuration Protocol) is how your router automatically gives each device the network settings it needs. In most homes, the router is the DHCP server. When a device connects, it asks for an address, the router offers one, the device accepts, and the router confirms. The device now has a temporary, private address on your LAN, plus the other settings it needs to reach the internet.
What the router hands out
A DHCP answer is a small bundle of settings, not just one number:
- A private IP address for the device, such as
192.168.1.23. It only means something inside your home. Public vs Private IP Address Explained covers the ranges. - A subnet mask, usually
255.255.255.0, which tells the device which addresses are "local." - A default gateway, normally the router's own LAN address, such as
192.168.1.1. This is where traffic for the internet goes. - DNS servers, the services that turn names like
example.cominto IP addresses. Often this is the router itself, which passes questions to your ISP's resolvers. - A lease time, which says how long the device may keep the address.
On Windows you can see the result with ipconfig /all. On a Mac or phone, open the Wi‑Fi network's details. The address you see there is your LAN address, not the public IP that websites see on the What Is My IP homepage. The router translates between the two.
Leases: why addresses are "borrowed"
DHCP addresses are leased, not owned. A home router commonly leases addresses for a day or so, but the length is a router setting and varies by brand.
Before the lease runs out, the device quietly asks to keep it. If the router agrees, nothing changes. If the device was away long enough for the lease to lapse, it may come back with a different number. That is normal, and it has nothing to do with the public address your ISP gives the router.
Your router may also get its WAN address from the ISP through DHCP. That is the same idea one level up. What Is a WAN IP Address? explains that side.
Common DHCP problems and what they mean
"169.254.x.x" or "Self-Assigned IP"
If a device asks for an address and nobody answers, it gives itself one from the 169.254.0.0/16 link-local range. Windows may say the adapter "doesn't have a valid IP configuration" or show "No internet," and macOS may warn about a self-assigned IP. A 169.254 address cannot reach the internet. It is a symptom: the device did not hear back from a DHCP server.
Usual causes:
- The router is still booting, frozen, or the Wi‑Fi link is weak.
- The router's DHCP server was switched off, or its pool of addresses is full.
- A cable, switch, mesh node, or powerline adapter in between is faulty.
Start by renewing the lease (steps below). If that fails, restart the router, wait for it to come back fully, and try again.
"IP address conflict"
Two devices ended up with the same LAN address, and both drop out intermittently. Usually someone typed a fixed address into a device that sits inside the router's DHCP pool, and the router later lent it to something else. Set the device back to automatic, or use a reservation (below).
Two DHCP servers on one network
If your own router sits behind the ISP's router and both hand out addresses, devices land on different subnets. Printers "disappear" and casting stops working. Let only one device run DHCP: put the second in access-point or bridge mode.
Connected, but pages will not load
If a device has a normal address and gateway but names will not resolve, the DNS server it was handed may be the problem. Site Down or DNS/IP Issue? walks through that split. If only one browser misbehaves, it may use its own DNS; see DNS over HTTPS for Normal Users.
How to renew a DHCP lease
Renewing asks the router for a fresh answer. It is safe and often enough.
- Windows: open Command Prompt and run
ipconfig /release, thenipconfig /renew. Your connection drops for a moment in between. - Mac: System Settings, then Network, select Wi‑Fi or Ethernet, click Details, open TCP/IP, and click Renew DHCP Lease.
- iPhone or iPad: Settings, then Wi‑Fi, tap the info button next to your network, and tap Renew Lease.
- Android, TVs, consoles: menus vary. Turning Wi‑Fi off and on, or restarting the device, forces a new request.
Once you are back online, the What Is My IP homepage should load and show your public address. If it does, the local side is working again.
DHCP reservation vs static IP
A printer, NAS, or console with port forwarding works best with a LAN address that never changes. Two options:
- DHCP reservation (recommended). In the router's settings, often under LAN or DHCP, you tie a device to an address. The router always offers that device the same number, and nothing on the device changes. No conflicts, because the router knows the address is taken.
- Manual static address on the device. You type the IP, mask, gateway, and DNS yourself. This works, but pick an address outside the router's DHCP pool, or you invite the conflict described above.
Reservations recognise devices by their hardware (MAC) address. Many phones use a private Wi‑Fi address per network, and some can rotate it, so a reserved phone may suddenly get a new number. Check that setting first.
Both options only fix the LAN address. A fixed public address is a separate ISP product. Static vs Dynamic IP for Home Internet covers when that is worth paying for.
A note on IPv6
On IPv6, many devices build their own addresses from what the router advertises, and some networks also use DHCPv6, so several IPv6 addresses on one device is normal. IPv4 vs IPv6: What Normal Users Need has the basics.
Bottom line
DHCP is the quiet service on your router that lends each device a private address, a gateway, and DNS servers for a limited time. A 169.254 address means no reply, a conflict means two devices share a number, and renewing the lease is the first fix to try. Use reservations for devices that need a stable LAN address, and check the What Is My IP homepage when you want to see the public side.